Implementing Linux native multipathing or DM-MPIO together with EMC PowerPath

puzzle

Guest Post

I’m delighted to say that this is another guest post from my good friend Nate Fuzi, who performs the same role as me for Violin but is based in the US instead of EMEA. Because he is American, Nate thinks that scones are called “biscuits”, that chips are called “fries” and that there is nothing – *nothing* – that cannot be improved with the simple addition of bacon. Clearly, something is fundamentally wrong with him – and yet he is like a brother to me. Like the strange, American step-brother I only see a few times a year and whom I cannot understand without the use of a translator. But he’s family all the same. So over to you Nate… and remember: Mom loved me more.

Remember when your parent answering your whiny “but whyyyyyyy???” with “Because I said so” was something you just had to accept? It meant there was no more explanation coming, and it was time for you to move on. Over the years, that answer broke down, and you grew confident you were owed more. And parents agreed: the more you demonstrated your ability to reason, the more reason you got to help you over the denial. It’s a sign of respect that we pay each other in adult life. And it can feel like disrespect if the reason offered feels weak or like it is intended to discourage further inquiry.

I was recently faced with solving what seemed a straightforward problem: take an existing Linux server running EMC’s multipathing software, PowerPath or “PP” as I will refer to it here, to access LUNs presented from that company’s SAN product, the VNX array, and attach and run Violin storage alongside the VNX. PP didn’t then support Violin arrays (still doesn’t at the time of this writing), so what was the client to do when they wanted to try out Violin’s AFA for their database environments? Just run PP and native Linux multipathing, called DM-MPIO, side by side, letting PP manage the VNX LUNs and DM-MPIO manage I/Os bound for Violin, right?

PowerPath versus DM-MPIO

PowerPath versus DM-MPIO

Wrong. Won’t work, I read. PowerPath does something at the HBA layer, I read a seemingly helpful web poster explain, that will corrupt either the VNX data or the Violin data. Well… maybe it will work, suggested another poster, but EMC might not support customers running in such a configuration. Others suggested ominously that PP and DM-MPIO don’t work well together… leaving it to the reader’s imagination what might result. I’m no master Googler, but I couldn’t find where anyone had put aside the rumors and vaguely threatening suggestions and actually tried it. Well, I did it, and I want to write about it so others know it can be done and how to do it because, well, those explanations I read didn’t stand up to question and felt like they were meant to scare me into not trying it. Of course I had to try it! Now, let’s be clear about what I am and am not saying: I am saying I have done this and it works. It’s in production at a customer site, running for months without issue. I am not saying that I have spoken to your EMC support rep and that you’ve been green-lighted to do this in your production environment. I’m not an EMC customer, and I don’t have a buddy in EMC support. So let’s consider this for informational purposes only for the time being.

First off, as several folks rightly pointed out, DM-MPIO could easily manage LUNs from both SAN products. Drop PP, configure DM-MPIO, and done. Well, that just sounds too simple. But it’s true: DM-MPIO has come a long way over the last few years and offers a pretty good set of features for free. PP costs money but is not without added value, as it does have additional configurability for reserve paths that become active in the event of a failure scenario, as well as IO distribution models beyond those offered by DM-MPIO, for example. My customer wanted to keep running PP, so this option was off the table for me.

Next up is the fun fact that PP advises you upon installation that you should “Blacklist all devices in /etc/multipath.conf and stop multipathd service”. The installer doesn’t say what will happen if you don’t do this, only that it is “*** IMPORTANT ***”. Check. Easy enough to ignore if this is the first thing you do. But if DM-MPIO is already running on the system and you try to start PP, it tells you this (verified in 5.7 and 6.0 only):

[root@host] # /etc/init.d/PowerPath start
Starting PowerPath:                                                      [FAILED]
Aborting PowerPath start since DM-Multipath is active.
Refer to PowerPath for Linux Installation and Administration Guide for more information

That’s a bummer. You actually have to stop multipathd and flush its paths before PP will start up. OK, I can do that. And, to be sure, you do NOT want both products attempting to manage IOs for the same device at the same time. That really is a bad thing. As we’ll see shortly, we might even want to segregate traffic across different FC ports, although this is strictly for optimization, not because you can’t mix traffic. But, as soon as we’ve installed the device-mapper-multipath-* packages, let’s honor this restriction right away by blacklisting the EMC devices in /etc/multipath.conf like this:

blacklist {
       devnode "^(control|vg|ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"    # standard stuff
       devnode "^hd[a-z][0-9]*"                                          # this line too
       device {
              vendor "DGC"
              product "*"
       }
       device {
              vendor "EMC"
              product "*"
       }
}

Note that the VNX line grew up in the Clariion company later acquired by EMC and presents a vendor string of “DGC”. Don’t ask me why. [Because the Clariion was a product from Data General Corporation? — flashdba :-)] It is my understanding that VMAX arrays do present “EMC” as their vendor string. Having done this, we want to explicitly except Violin devices from getting blacklisted:

blacklist_exceptions {
       device {
              vendor "VIOLIN"
              product "*"
       }
}

This isn’t completely necessary, but it does make clear our intentions: don’t manage VNX/EMC devices but do manage Violin devices. Having both entries in the file means that adding some third storage product to the FC SAN won’t cause it to get picked up by DM-MPIO without us consciously making it so. Belt and suspenders, they used to say.

Verify your multipath configuration without actually running it. Do this by adding the “-d” flag to your multipath command:

[root@host] # multipath -v3 -d

The “-v3″ flag gives us a verbose parsing of the configuration file so we can see each device and whether, what, and why DM-MPIO is going to do that with device. Make changes ad nauseum, and once you like what you see, run the command without “-d”, and create your multipath devices.

Cool. But remember when PP refused to start up earlier, saying DM-MPIO was found running? Guess what: PP’s inexplicable method of editing your /etc/rc.d/rc.sysinit script to insert its startup lines means it doesn’t attempt to start up until after DM-MPIO gets started on reboot. (Take a look for yourself; it’s there. It also makes you manually start PP if you apply a kernel update that resets the contents of rc.sysinit, at which point it reinserts the startup lines. Sweet.) How to get around this? I’m sure there are lots of solutions. I created a script to flush existing multipaths and start up PP in /etc/init.d and linked it as /etc/rc.d/rc3.d/S86PowerPath. This makes it so PP gets called just prior to DM-MPIO, and each is happy. The later call in /etc/rc.d/rc.sysinit is then redundant but causes no harm. I suppose you could almost as easily edit the rc.sysinit script to remove the check–just remember to make the same edit if/when you update PP.

Now, what was that I said a bit ago about segregating traffic on different HBA ports? This is not required; no magic is happening on the HBA with either product. Each one will discover the devices it is concerned with via its own callout routine and handle that device how you configure it to. But let’s imagine you have 4 FC ports on your host and choose to allow PP and DM-MPIO to each manage devices across all those ports. Neither will be aware what the other is doing in terms of trying to optimize IO distribution across all paths available, and you could well end up shooting yourself in the foot with sub-optimal end results. Segregating traffic also allows you to set different HBA queue depths or optimization settings as recommended by each storage vendor, and we all want to comply with best practices, right?!

Conclusion

None of this is meant to disparage EMC. Well, OK: the part about having the PowerPath startup script insert lines into /etc/rc.d/rc.sysinit is meant to disparage. I think that’s archaic and clunky. I have to believe there’s a more elegant way to do that today. I do hope I save some other soul the frustration I went through determining if this could be done and then how. If anyone has implemented more elegant solutions, I’d love to read about them.

New Cookbook: Oracle Linux 6 Update 5 within an Oracle VM Template

Oracle-VMI’ve posted a new installation cookbook for using Oracle within a virtual machine running on Oracle VM. Surprisingly, I was unable to come up with a satisfactory method of accessing external storage that did not involve the use of Oracle ASMLib

Oracle Linux 6 Update 5 within an Oracle VM Template

Viewing ASM trace files in VIM: Which Way Do You Use?

cafepress_womens_cap_sleeve_tshirt

A couple of people have asked me recently about a classic problem that most DBAs know: how to view ASM trace files in the VIM editor when the filenames start with a + character. To my surprise, there are actually quite a few different ways of doing it. Since it’s come up, I thought I’d list a few of them here… If you have another one to add, feel free to comment. I know that most people reading this already have an answer, I’m just interested in who uses the most efficient one…

The Problem

VIM is a text editor used in many different operating systems. You know the one, it’s incredibly powerful, utterly incomprehensible to the newcomer… and will forever have more options than you can remember. I mean, just check out the cheat sheet:

People love or hate vim (I love it), but it’s often used on Linux systems simply because it’s always there. The problem comes when you want to look at ASM trace files, because they have a silly name:

oracle@server3 trace]$ pwd
/u01/app/oracle/diag/asm/+asm/+ASM/trace
[oracle@server3 trace]$ ls -l +ASM_ora_27425*
-rw-r----- 1 oracle oinstall 20625 Aug 20 15:42 +ASM_ora_27425.trc
-rw-r----- 1 oracle oinstall   528 Aug 20 15:42 +ASM_ora_27425.trm

Oracle trace files tend to have names in the format <oracle-sid>-<process-name>-<process-id>.trc, which is fine until the Oracle SID is that of the Automatic Storage Management instance, i.e. “+ASM”.

It’s that “+” prefix character that does it:

[oracle@server3 trace]$ vim +ASM_ora_27425.trc

Error detected while processing command line:
E492: Not an editor command: ASM_ora_27425.trc
Press ENTER or type command to continue

Why does this happen? Well because in among the extensive options of vim are to be found the following:

[oracle@server3 trace]$ man vim
...
OPTIONS
       The  options may be given in any order, before or after filenames.  Options without an argument can be combined after a
       single dash.

       +[num]      For the first file the cursor will be positioned on line "num".  If "num" is missing, the  cursor  will  be
                   positioned on the last line.

       +/{pat}     For  the first file the cursor will be positioned on the first occurrence of {pat}.  See ":help search-pat-
                   tern" for the available search patterns.

       +{command}
...

So… the plus character is actually being interpreted by VIM as an option. Surely we can just escape it then, right?

[oracle@server3 trace]$ vim \+ASM_ora_27425.trc

Error detected while processing command line:
E492: Not an editor command: ASM_ora_27425.trc
Press ENTER or type command to continue

Nope. And neither single nor double quotes around the filename work either. So what are the options?

Solution 1: Make Sure The “+” Isn’t The Prefix

Simple, but effective. If the + character isn’t leading the filename, VIM won’t try to interpret it. So instead of a relative filename, I could use the absolute:

[oracle@server3 trace]$ vi /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_27425.trc

Or even just use a ./ to denote the current directory:

[oracle@server3 trace]$ vi ./+ASM_ora_27425.trc

Solution 2: Double Dash

Even simpler, but less well known (I think?) is the double-dash or hyphen option. If you browse the VIM man page a little further on, you’ll find this:

[oracle@server3 trace]$ man vim
...
 --          Denotes  the end of the options.  Arguments after this will be handled as a file name.  This can be used to
                   edit a filename that starts with a ’-’.
...

And it works perfectly:

[oracle@server3 trace]$ vi -- +ASM_ora_27425.trc

Solution 3: Use Find and -Exec

Another, slightly messy option is to use the find command to send the file to VIM. I know people who still do this, despite it being more work than the other options – sometimes a lazy hack can become unconscious habit:

[oracle@server3 trace]$ find . -name +ASM_ora_27425.trc -exec vi {} \;

In fact, I actually know somebody who used to look up the file’s inode number and then pass that into find:

[oracle@server3 trace]$ ls -li +ASM_ora_27425*
138406 -rw-r----- 1 oracle oinstall 20625 Aug 20 15:42 +ASM_ora_27425.trc
138407 -rw-r----- 1 oracle oinstall   528 Aug 20 15:42 +ASM_ora_27425.trm
[oracle@server3 trace]$ find . -inum 138406 -exec vi {} \;

Luckily nobody will ever know who that somebody is*.

Solution 4: Rename It

My least favourite option, but it’s actually quite efficient. Simple create a copy of the file with a new name that doesn’t contain a plus – luckily the cp command doesn’t care about the + prefix:

[oracle@server3 trace]$ cp +ASM_ora_27425.trc me.trc
[oracle@server3 trace]$ vi me.trc

Of course, you’ll want to tidy up that new file afterwards and not just leave it lying around… won’t you?

Less Is More

Maybe you’re not the sort of person that likes to use VIM. Maybe you prefer the more basic OS tools like cat (which works fine on ASM trace files), or more (which doesn’t), or even less.

In fact, less has pretty much the same options as VIM, which means you can use all of the above solutions with it. If you are using more, you cannot pass this a double dash but the others will work. And if you’re using cat, good luck to you… I hope you have a big screen.

* Yes, of course, it was me.

Oracle 12.1.0.2 ASM Filter Driver: Advanced Format Fail

wrong-way

In my previous post on the subject of the new ASM Filter Driver (AFD) feature introduced in Oracle’s 12.1.0.2 patchset, I installed the AFD to see how it fulfilled its promise that it “filters out all non-Oracle I/Os which could cause accidental overwrites“. However, because I was ten minutes away from my summer vacation at the point of finishing that post, I didn’t actually get round to writing about what happens when you try and create ASM diskgroups on the devices it presents.

Obviously I’ve spent the intervening period constantly worrying about this oversight – indeed, it was only through the judicious application of good food and drink plus some committed relaxation in the sun that I was able to pull through. However, I’m back now and it seems like time to rectify that mistake. So here goes.

Creating ASM Diskgroups with the ASM Filter Driver

It turns out I need not have worried, because it doesn’t work right now… at least, not for me. Here’s why:

First of all, I installed Oracle 12.1.0.2 Grid Infrastructure. I then labelled some block devices presented from my Violin storage array. As I’ve already pasted all the output from those two steps in the previous post, I won’t repeat myself.

The next step is therefore to create a diskgroup. Since I’ve only just come back from holiday and so I’m still half brain-dead, I’ll choose the simple route and fire up the ASM Configuration Assistant (ASMCA) so that I don’t have to look up any of that nasty SQL. Here goes:

afd_create

But guess what happened when I hit the OK button? It failed, bigtime. Here’s the alert log – if you don’t like huge amounts of meaningless text I suggest you skip down… a lot… (although thinking about it, my entire blog could be described as meaningless text):

SQL> CREATE DISKGROUP DATA EXTERNAL REDUNDANCY  DISK 'AFD:DATA1' SIZE 72704M ,
'AFD:DATA2' SIZE 72704M ,
'AFD:DATA3' SIZE 72704M ,
'AFD:DATA4' SIZE 72704M ,
'AFD:DATA5' SIZE 72704M ,
'AFD:DATA6' SIZE 72704M ,
'AFD:DATA7' SIZE 72704M ,
'AFD:DATA8' SIZE 72704M  ATTRIBUTE 'compatible.asm'='12.1.0.0.0','au_size'='1M' /* ASMCA */
Fri Jul 25 16:25:33 2014
WARNING: Library 'AFD Library - Generic , version 3 (KABI_V3)' does not support advanced format disks
Fri Jul 25 16:25:33 2014
NOTE: Assigning number (1,0) to disk (AFD:DATA1)
NOTE: Assigning number (1,1) to disk (AFD:DATA2)
NOTE: Assigning number (1,2) to disk (AFD:DATA3)
NOTE: Assigning number (1,3) to disk (AFD:DATA4)
NOTE: Assigning number (1,4) to disk (AFD:DATA5)
NOTE: Assigning number (1,5) to disk (AFD:DATA6)
NOTE: Assigning number (1,6) to disk (AFD:DATA7)
NOTE: Assigning number (1,7) to disk (AFD:DATA8)
NOTE: initializing header (replicated) on grp 1 disk DATA1
NOTE: initializing header (replicated) on grp 1 disk DATA2
NOTE: initializing header (replicated) on grp 1 disk DATA3
NOTE: initializing header (replicated) on grp 1 disk DATA4
NOTE: initializing header (replicated) on grp 1 disk DATA5
NOTE: initializing header (replicated) on grp 1 disk DATA6
NOTE: initializing header (replicated) on grp 1 disk DATA7
NOTE: initializing header (replicated) on grp 1 disk DATA8
NOTE: initializing header on grp 1 disk DATA1
NOTE: initializing header on grp 1 disk DATA2
NOTE: initializing header on grp 1 disk DATA3
NOTE: initializing header on grp 1 disk DATA4
NOTE: initializing header on grp 1 disk DATA5
NOTE: initializing header on grp 1 disk DATA6
NOTE: initializing header on grp 1 disk DATA7
NOTE: initializing header on grp 1 disk DATA8
NOTE: Disk 0 in group 1 is assigned fgnum=1
NOTE: Disk 1 in group 1 is assigned fgnum=2
NOTE: Disk 2 in group 1 is assigned fgnum=3
NOTE: Disk 3 in group 1 is assigned fgnum=4
NOTE: Disk 4 in group 1 is assigned fgnum=5
NOTE: Disk 5 in group 1 is assigned fgnum=6
NOTE: Disk 6 in group 1 is assigned fgnum=7
NOTE: Disk 7 in group 1 is assigned fgnum=8
NOTE: initiating PST update: grp = 1
Fri Jul 25 16:25:33 2014
GMON updating group 1 at 1 for pid 7, osid 16745
NOTE: group DATA: initial PST location: disk 0000 (PST copy 0)
NOTE: set version 1 for asmCompat 12.1.0.0.0
Fri Jul 25 16:25:33 2014
NOTE: PST update grp = 1 completed successfully
NOTE: cache registered group DATA 1/0xD9B6AE8D
NOTE: cache began mount (first) of group DATA 1/0xD9B6AE8D
NOTE: cache is mounting group DATA created on 2014/07/25 16:25:33
NOTE: cache opening disk 0 of grp 1: DATA1 label:DATA1
NOTE: cache opening disk 1 of grp 1: DATA2 label:DATA2
NOTE: cache opening disk 2 of grp 1: DATA3 label:DATA3
NOTE: cache opening disk 3 of grp 1: DATA4 label:DATA4
NOTE: cache opening disk 4 of grp 1: DATA5 label:DATA5
NOTE: cache opening disk 5 of grp 1: DATA6 label:DATA6
NOTE: cache opening disk 6 of grp 1: DATA7 label:DATA7
NOTE: cache opening disk 7 of grp 1: DATA8 label:DATA8
NOTE: cache creating group 1/0xD9B6AE8D (DATA)
NOTE: cache mounting group 1/0xD9B6AE8D (DATA) succeeded
WARNING: cache read a corrupt block: group=1(DATA) dsk=0 blk=1 disk=0 (DATA1) incarn=3493224069 au=0 blk=1 count=1
Fri Jul 25 16:25:33 2014
Errors in file /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc:
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
NOTE: a corrupted block from group DATA was dumped to /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc
WARNING: cache read (retry) a corrupt block: group=1(DATA) dsk=0 blk=1 disk=0 (DATA1) incarn=3493224069 au=0 blk=1 count=1
Fri Jul 25 16:25:33 2014
Errors in file /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc:
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
WARNING: cache read (retry) a corrupt block: group=1(DATA) dsk=0 blk=1 disk=0 (DATA1) incarn=3493224069 au=11 blk=1 count=1
Fri Jul 25 16:25:33 2014
Errors in file /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc:
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
NOTE: a corrupted block from group DATA was dumped to /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc
WARNING: cache read (retry) a corrupt block: group=1(DATA) dsk=0 blk=1 disk=0 (DATA1) incarn=3493224069 au=11 blk=1 count=1
Fri Jul 25 16:25:33 2014
Errors in file /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc:
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ERROR: cache failed to read group=1(DATA) dsk=0 blk=1 from disk(s): 0(DATA1) 0(DATA1)
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]

NOTE: cache initiating offline of disk 0 group DATA
NOTE: process _user16745_+asm (16745) initiating offline of disk 0.3493224069 (DATA1) with mask 0x7e in group 1 (DATA) with client assisting
NOTE: initiating PST update: grp 1 (DATA), dsk = 0/0xd0365e85, mask = 0x6a, op = clear
Fri Jul 25 16:25:34 2014
GMON updating disk modes for group 1 at 2 for pid 7, osid 16745
ERROR: disk 0(DATA1) in group 1(DATA) cannot be offlined because the disk group has external redundancy.
Fri Jul 25 16:25:34 2014
ERROR: too many offline disks in PST (grp 1)
Fri Jul 25 16:25:34 2014
ERROR: no read quorum in group: required 1, found 0 disks
ERROR: Could not read PST for grp 1. Force dismounting the disk group.
Fri Jul 25 16:25:34 2014
NOTE: halting all I/Os to diskgroup 1 (DATA)
Fri Jul 25 16:25:34 2014
ERROR: no read quorum in group: required 1, found 0 disks
ASM Health Checker found 1 new failures
Fri Jul 25 16:25:36 2014
ERROR: no read quorum in group: required 1, found 0 disks
Fri Jul 25 16:25:36 2014
ERROR: Could not read PST for grp 1. Force dismounting the disk group.
Fri Jul 25 16:25:36 2014
ERROR: no read quorum in group: required 1, found 0 disks
ERROR: Could not read PST for grp 1. Force dismounting the disk group.
Fri Jul 25 16:25:36 2014
ERROR: no read quorum in group: required 1, found 0 disks
ERROR: Could not read PST for grp 1. Force dismounting the disk group.
Fri Jul 25 16:25:37 2014
NOTE: AMDU dump of disk group DATA initiated at /u01/app/oracle/diag/asm/+asm/+ASM/trace
Errors in file /u01/app/oracle/diag/asm/+asm/+ASM/trace/+ASM_ora_16745.trc  (incident=3257):
ORA-15335: ASM metadata corruption detected in disk group 'DATA'
ORA-15130: diskgroup "DATA" is being dismounted
ORA-15066: offlining disk "DATA1" in group "DATA" may result in a data loss
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]
Incident details in: /u01/app/oracle/diag/asm/+asm/+ASM/incident/incdir_3257/+ASM_ora_16745_i3257.trc
Fri Jul 25 16:25:37 2014
Sweep [inc][3257]: completed
Fri Jul 25 16:25:37 2014
SQL> alter diskgroup DATA check
System State dumped to trace file /u01/app/oracle/diag/asm/+asm/+ASM/incident/incdir_3257/+ASM_ora_16745_i3257.trc
NOTE: erasing header (replicated) on grp 1 disk DATA1
NOTE: erasing header (replicated) on grp 1 disk DATA2
NOTE: erasing header (replicated) on grp 1 disk DATA3
NOTE: erasing header (replicated) on grp 1 disk DATA4
NOTE: erasing header (replicated) on grp 1 disk DATA5
NOTE: erasing header (replicated) on grp 1 disk DATA6
NOTE: erasing header (replicated) on grp 1 disk DATA7
NOTE: erasing header (replicated) on grp 1 disk DATA8
NOTE: erasing header on grp 1 disk DATA1
NOTE: erasing header on grp 1 disk DATA2
NOTE: erasing header on grp 1 disk DATA3
NOTE: erasing header on grp 1 disk DATA4
NOTE: erasing header on grp 1 disk DATA5
NOTE: erasing header on grp 1 disk DATA6
NOTE: erasing header on grp 1 disk DATA7
NOTE: erasing header on grp 1 disk DATA8
Fri Jul 25 16:25:37 2014
NOTE: cache dismounting (clean) group 1/0xD9B6AE8D (DATA)
NOTE: messaging CKPT to quiesce pins Unix process pid: 16745, image: oracle@server3.local (TNS V1-V3)
NOTE: dbwr not being msg'd to dismount
NOTE: LGWR not being messaged to dismount
NOTE: cache dismounted group 1/0xD9B6AE8D (DATA)
NOTE: cache ending mount (fail) of group DATA number=1 incarn=0xd9b6ae8d
NOTE: cache deleting context for group DATA 1/0xd9b6ae8d
Fri Jul 25 16:25:37 2014
GMON dismounting group 1 at 3 for pid 7, osid 16745
Fri Jul 25 16:25:37 2014
NOTE: Disk DATA1 in mode 0x7f marked for de-assignment
NOTE: Disk DATA2 in mode 0x7f marked for de-assignment
NOTE: Disk DATA3 in mode 0x7f marked for de-assignment
NOTE: Disk DATA4 in mode 0x7f marked for de-assignment
NOTE: Disk DATA5 in mode 0x7f marked for de-assignment
NOTE: Disk DATA6 in mode 0x7f marked for de-assignment
NOTE: Disk DATA7 in mode 0x7f marked for de-assignment
NOTE: Disk DATA8 in mode 0x7f marked for de-assignment
ERROR: diskgroup DATA was not created
ORA-15018: diskgroup cannot be created
ORA-15335: ASM metadata corruption detected in disk group 'DATA'
ORA-15130: diskgroup "DATA" is being dismounted
Fri Jul 25 16:25:37 2014
ORA-15032: not all alterations performed
ORA-15066: offlining disk "DATA1" in group "DATA" may result in a data loss
ORA-15001: diskgroup "DATA" does not exist or is not mounted
ORA-15196: invalid ASM block header [kfc.c:29297] [endian_kfbh] [2147483648] [1] [0 != 1]

Now then. First of all, thanks for making it this far – I promise not to do that again in this post. Secondly, in case you really did just hit page down *a lot* you might want to skip back up and look for the bits I’ve conveniently highlighted in red. Specifically, this bit:

WARNING: Library 'AFD Library - Generic , version 3 (KABI_V3)' does not support advanced format disks

Many modern storage platforms use Advanced Format – if you want to know what that means, read here. The idea that AFD doesn’t support advanced format is somewhat alarming – and indeed incorrect, according to interactions I have subsequently had with Oracle’s ASM Product Management people. From what I understand, the problem is tracked as bug 19297177 (currently unpublished) and is caused by AFD incorrectly checking the physical blocksize of the storage device (4k) instead of the logical block size (which was 512 bytes). I currently have a request open with Oracle Support for the patch, so when that arrives I will re-test and add another blog article.

Until then, I guess I might as well take another well-earned vacation?

Oracle 12.1.0.2 ASM Filter Driver: First Impressions

This is a very quick post, because I’m about to log off and take an extended summer holiday (or vacation as my crazy American friends call it… but then they call football  “soccer” too). Before I go, I wanted to document my initial findings with the new ASM Filter Driver feature introduced in this week’s 12.1.o.2 patchset.

Currently a Linux-only feature, the ASM Filter Driver (or AFD) is a replacement for ASMLib and is described by Oracle as follows:

Oracle ASM Filter Driver (Oracle ASMFD) is a kernel module that resides in the I/O path of the Oracle ASM disks. Oracle ASM uses the filter driver to validate write I/O requests to Oracle ASM disks.

The Oracle ASMFD simplifies the configuration and management of disk devices by eliminating the need to rebind disk devices used with Oracle ASM each time the system is restarted.

The Oracle ASM Filter Driver rejects any I/O requests that are invalid. This action eliminates accidental overwrites of Oracle ASM disks that would cause corruption in the disks and files within the disk group. For example, the Oracle ASM Filter Driver filters out all non-Oracle I/Os which could cause accidental overwrites.

Interesting, eh? So let’s find out how that works.

Installation

I found this a real pain as you need to have 12.1.0.2 installed before the AFD is available to label your disks, yet the default OUI mode wants to create an ASM diskgroup… and you cannot do that without any labelled disks.

The only solution I could come up with was to perform a software-only install, which in itself is a pain. I’ll skip the numerous screenshots of that part though and just skip straight to the bit where I have 12.1.0.2 Grid Infrastructure installed.

I’m following these instructions because I am using a single-instance Oracle Restart system rather than a true cluster.

First of all we need to do this:

[oracle@server3 ~]$ $ORACLE_HOME/bin/asmcmd dsset 'AFD:*'

[oracle@server3 ~]$ $ORACLE_HOME/bin/asmcmd dsget
parameter:AFD:*
profile:AFD:*
[oracle@server3 ~]$ srvctl config asm
ASM home: 
Password file:
ASM listener: LISTENER
Spfile: /u01/app/oracle/admin/+ASM/pfile/spfile+ASM.ora
ASM diskgroup discovery string: AFD:*

Then we need to stop HAS and run the AFD_CONFIGURE command:

[root@server3 ~]# $ORACLE_HOME/bin/crsctl stop has -f
CRS-2791: Starting shutdown of Oracle High Availability Services-managed resources on 'server3'
CRS-2673: Attempting to stop 'ora.asm' on 'server3'
CRS-2673: Attempting to stop 'ora.evmd' on 'server3'
CRS-2673: Attempting to stop 'ora.LISTENER.lsnr' on 'server3'
CRS-2677: Stop of 'ora.LISTENER.lsnr' on 'server3' succeeded
CRS-2677: Stop of 'ora.evmd' on 'server3' succeeded
CRS-2677: Stop of 'ora.asm' on 'server3' succeeded
CRS-2673: Attempting to stop 'ora.cssd' on 'server3'
CRS-2677: Stop of 'ora.cssd' on 'server3' succeeded
CRS-2793: Shutdown of Oracle High Availability Services-managed resources on 'server3' has completed
CRS-4133: Oracle High Availability Services has been stopped.

[root@server3 ~]# $ORACLE_HOME/bin/asmcmd afd_configure
Connected to an idle instance.
AFD-627: AFD distribution files found.
AFD-636: Installing requested AFD software.
AFD-637: Loading installed AFD drivers.
AFD-9321: Creating udev for AFD.
AFD-9323: Creating module dependencies - this may take some time.
AFD-9154: Loading 'oracleafd.ko' driver.
AFD-649: Verifying AFD devices.
AFD-9156: Detecting control device '/dev/oracleafd/admin'.
AFD-638: AFD installation correctness verified.
Modifying resource dependencies - this may take some time.
ASMCMD-9524: AFD configuration failed 'ERROR: OHASD start failed'

Er… that’s not really what I had in mind. But hey, let’s carry on regardless:

[root@server3 oracleafd]# $ORACLE_HOME/bin/asmcmd afd_state
Connected to an idle instance.
ASMCMD-9526: The AFD state is 'LOADED' and filtering is 'DEFAULT' on host 'server3.local'

[root@server3 oracleafd]# $ORACLE_HOME/bin/crsctl start has
CRS-4123: Oracle High Availability Services has been started.

Ok it seems to be working. I wonder what it’s done?

Investigation

The first thing I notice is some Oracle kernel modules have been loaded:

[root@server3 ~]# lsmod | grep ora
oracleafd             208499  1
oracleacfs           3307969  0
oracleadvm            506254  0
oracleoks             505749  2 oracleacfs,oracleadvm

I also see that, just like ASMLib, a driver has been plonked into the /opt/oracle/extapi directory:

[root@server3 1]# find /opt/oracle/extapi -ls
2752765    4 drwxr-xr-x   3 root     root         4096 Jul 25 15:15 /opt/oracle/extapi
2752766    4 drwxr-xr-x   3 root     root         4096 Jul 25 15:15 /opt/oracle/extapi/64
2753508    4 drwxr-xr-x   3 root     root         4096 Jul 25 15:15 /opt/oracle/extapi/64/asm
2756532    4 drwxr-xr-x   3 root     root         4096 Jul 25 15:15 /opt/oracle/extapi/64/asm/orcl
2756562    4 drwxr-xr-x   2 root     root         4096 Jul 25 15:15 /opt/oracle/extapi/64/asm/orcl/1
2756578  268 -rwxr-xr-x   1 oracle   dba        272513 Jul 25 15:15 /opt/oracle/extapi/64/asm/orcl/1/libafd12.so

And again, just like ASMLib, there is a new directory under /dev called /dev/oracleafd (whereas for ASMLib it’s called /dev/oracleasm):

[root@server3 ~]# ls -la /dev/oracleafd/
total 0
drwxrwx---  3 oracle dba      80 Jul 25 15:15 .
drwxr-xr-x 21 root   root  15820 Jul 25 15:15 ..
brwxrwx---  1 oracle dba  249, 0 Jul 25 15:15 admin
drwxrwx---  2 oracle dba      40 Jul 25 15:15 disks

The disks directory is currently empty. Maybe I should create some AFD devices and see what happens?

Labelling

So let’s look at my Violin devices and see if I can label them:

root@server3 mapper]# ls -l /dev/mapper
total 0
crw-rw---- 1 root root 10, 236 Jul 11 16:52 control
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data1 -> ../dm-3
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data2 -> ../dm-4
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data3 -> ../dm-5
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data4 -> ../dm-6
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data5 -> ../dm-7
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data6 -> ../dm-8
lrwxrwxrwx 1 root root       7 Jul 25 15:49 data7 -> ../dm-9
lrwxrwxrwx 1 root root       8 Jul 25 15:49 data8 -> ../dm-10
lrwxrwxrwx 1 root root       7 Jul 11 16:53 VolGroup-lv_home -> ../dm-2
lrwxrwxrwx 1 root root       7 Jul 11 16:53 VolGroup-lv_root -> ../dm-0
lrwxrwxrwx 1 root root       7 Jul 11 16:52 VolGroup-lv_swap -> ../dm-1

The documentation appears to be incorrect here, when it says to use the command $ORACLE_HOME/bin/afd_label. It’s actually $ORACLE_HOME/bin/asmcmd with the first parameter afd_label. I’m going to label the devices called /dev/mapper/data*:

[root@server3 mapper]# for lun in 1 2 3 4 5 6 7 8; do
> asmcmd afd_label DATA$lun /dev/mapper/data$lun
> done
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.
Connected to an idle instance.

root@server3 mapper]# asmcmd afd_lsdsk
Connected to an idle instance.
--------------------------------------------------------------------------------
Label                     Filtering   Path
================================================================================
DATA1                       ENABLED   /dev/mapper/data1
DATA2                       ENABLED   /dev/mapper/data2
DATA3                       ENABLED   /dev/mapper/data3
DATA4                       ENABLED   /dev/mapper/data4
DATA5                       ENABLED   /dev/mapper/data5
DATA6                       ENABLED   /dev/mapper/data6
DATA7                       ENABLED   /dev/mapper/data7
DATA8                       ENABLED   /dev/mapper/data8

That seemed to work ok. So what’s going on in the /dev/oracleafd/disks directory now?

[root@server3 ~]# ls -l /dev/oracleafd/disks/
total 32
-rw-r--r-- 1 root root 26 Jul 25 15:52 DATA1
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA2
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA3
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA4
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA5
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA6
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA7
-rw-r--r-- 1 root root 26 Jul 25 15:49 DATA8

There they are, just like with ASMLib. But look at the permissions, they are all owned by root with read-only privs for other users. In an ASMLib environment these devices are owned by oracle:dba, which means non-Oracle processes can write to them and corrupt them in some situations. Is this how Oracle claims the AFD protects devices?

I haven’t had time to investigate further but I assume that the database will access the devices via this mysterious block device:

[oracle@server3 oracleafd]$ ls -l /dev/oracleafd/admin
brwxrwx--- 1 oracle dba 249, 0 Jul 25 16:25 /dev/oracleafd/admin

It will be interesting to find out.

Distruction

Of course, if you are logged in as root you aren’t going to be protected from any crazy behaviour:

[root@server3 ~]# cd /dev/oracleafd/disks
[root@server3 disks]# ls -l
total 496
-rw-r--r-- 1 root root 475877 Jul 25 16:40 DATA1
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA2
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA3
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA4
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA5
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA6
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA7
-rw-r--r-- 1 root root     26 Jul 25 15:49 DATA8
[root@server3 disks]# od -c -N 256 DATA8
0000000   /   d   e   v   /   m   a   p   p   e   r   /   d   a   t   a
0000020   8  \n
0000032
[root@server3 disks]# dmesg >> DATA8
[root@server3 disks]# od -c -N 256 DATA8
0000000   /   d   e   v   /   m   a   p   p   e   r   /   d   a   t   a
0000020   8   \n   z   r   d   b   t   e   2  l   I   n   i   t   i   a
0000040   l   i   z   i   n   g       c   g   r   o   u   p       s   u
0000060   b   s   y   s       c   p   u   s   e   t  \n   I   n   i   t
0000100   i   a   l   i   z   i   n   g       c   g   r   o   u   p
0000120   s   u   b   s   y   s       c   p   u  \n   L   i   n   u   x
0000140       v   e   r   s   i   o   n       3   .   8   .   1   3   -
0000160   2   6   .   2   .   3   .   e   l   6   u   e   k   .   x   8
0000200   6   _   6   4       (   m   o   c   k   b   u   i   l   d   @
0000220   c   a   -   b   u   i   l   d   4   4   .   u   s   .   o   r
0000240   a   c   l   e   .   c   o   m   )       (   g   c   c       v
0000260   e   r   s   i   o   n       4   .   4   .   7       2   0   1
0000300   2   0   3   1   3       (   R   e   d       H   a   t       4
0000320   .   4   .   7   -   3   )       (   G   C   C   )       )
0000340   #   2       S   M   P       W   e   d       A   p   r       1
0000360   6       0   2   :   5   1   :   1   0       P   D   T       2
0000400

Proof, if ever you need it, that root access is still the fastest and easiest route to total disaster…

The Ultimate Guide To Oracle with Advanced Format 4k

fud

It’s a brave thing, calling something the “Ultimate Guide To …” as it can leave you open to criticism that it’s anything but. However, this topic – of how Oracle runs on Advanced Format storage systems and which choices have which consequences – is one I’ve been learning for two years now, so this really is everything I know. And from my desperate searching of the internet, plus discussions with people who are usually much knowledgeable than me, I’ve come to the conclusion that nobody else really understands it.

In fact, you could say that it’s a topic full of confusion – and if you browsed the support notes on My Oracle Support you’d definitely come to that conclusion. Part of that confusion is unfortunately FUD, spread by storage vendors who do not (yet) support Advanced Format and therefore benefit from scaring customers away from it. Be under no illusions, with the likes of Western DigitalHGST and Seagate all signed up to Advanced Format, plus Violin Memory and EMC’s XtremIO both using it, it’s something you should embrace rather than avoid.

However, to try and lessen the opportunity for those competitors to point and say “Look how complicated it is!”, I’ve split my previous knowledge repository into two: a high-level page and an Oracle on 4k deep dive. It’s taken me years to work all this stuff out – and days to write it all down, so I sincerely hope it saves someone else a lot of time and effort…!

Advanced Format with 4k Sectors

Advanced Format: Oracle on 4k Deep Dive

New installation cookbook for SUSE Linux Enterprise Server 11 SP3

Exactly what it says on the tin, I’ve added a new installation cookbook for SUSE 11 SP3 which creates Violin on a set of 4k devices.

I’ve started setting the add_random tunable of the noop I/O scheduler because it seems to give a boost in performance during benchmarking runs. If I can find the time, I will blog about this at some point…

For more details read this document from Red Hat.

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