On 8/10/2010 12:21 PM, Greg Smith wrote:
Scott Carey wrote:
Also, the amount of data at risk in a power loss varies between
drives. For Intel's drives, its a small chunk of data ( < 256K).
For some other drives, the cache can be over 30MB of outstanding writes.
For some workloads this is acceptable
No, it isn't ever acceptable. You can expect the type of data loss
you get when a cache fails to honor write flush calls results in
catastrophic database corruption. It's not "I lost the last few
seconds"; it's "the database is corrupted and won't start" after a
crash. This is why we pound on this topic on this list. A SSD that
fails to honor flush requests is completely worthless for anything
other than toy databases. You can expect significant work to recover
any portion of your data after the first unexpected power loss under
heavy write load in this environment, during which you're down. We do
database corruption recovery at 2ndQuadrant; while I can't talk about
the details of some recent incidents, I am not speaking theoretically
when I warn about this.
What about putting indexes on them? If the drive fails and drops writes
on those, they could be rebuilt - assuming your system can function
without the index(es) temporarily.
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.
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