Something is wrong with how Oracle tracks I/O statistics in AWR – here's the reproducible anomaly, the evidence it's real and the investigation into what causes it.
Author: flashdba
Understanding Flash: Unpredictable Write Performance
Not all NAND flash writes are equal. MLC flash has fast pages and slow pages, creating unpredictable write latency unless the storage controller manages them intelligently. This article explains why write performance varies and what enterprise arrays do about it.
Oracle AWR Reports: When Averages Lie
An ERP database showing intermittent slowdowns looked fine in AWR – because AWR averages hide latency spikes. Here's why averages mislead and what to look at instead.
Understanding Flash: The Write Cliff
When flash garbage collection cannot keep pace with incoming writes, performance falls off a cliff. This article explains background versus active garbage collection, write amplification and why predictability matters more than peak speed.
Postcard from Oracle OpenWorld 2014: The Oracle FS1 Flash Array
A couple of weeks ago I wrote a post about my trip to Oracle OpenWorld 2014 and the surprise announcement of the Oracle FS1 Flash Array. I posted it on the Violin Memory corporate website here: http://www.violin-memory.com/blog/postcard-oracle-openworld-2014-the-oracle-fs1-flash-array/ Follow the link to find out whether I thought it was the most amazing product in the history … Continue reading Postcard from Oracle OpenWorld 2014: The Oracle FS1 Flash Array
Understanding Flash: Garbage Collection Matters
NAND flash can only be erased at the block level, not the page level. Garbage collection is the process that recycles stale pages to keep a flash system writable – and without it, performance collapses. This article explains why.
Understanding Flash: The Flash Translation Layer
The flash translation layer is the hidden software layer that makes NAND flash usable as enterprise storage. This article explains logical block mapping, wear levelling, garbage collection and write amplification.
Oracle, Parallelism and Direct Path Reads… on Flash
Oracle's parallel query engine behaves differently on flash than on spinning disk – direct path reads change the picture in ways that DBAs tuning for traditional storage won't expect.
Viewing ASM trace files in VIM: Which Way Do You Use?
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 … Continue reading Viewing ASM trace files in VIM: Which Way Do You Use?
Oracle 12.1.0.2 ASM Filter Driver: Advanced Format Fail
The ASM Filter Driver introduced in Oracle 12.1.0.2 as a replacement for ASMLib has a critical flaw: it fails entirely with 4k native Advanced Format devices.
flashdba 