On 12/12/2012 09:44 AM, Evgeny Shishkin
wrote:
So far, more than a year already, i bought consumer ssds with
300-400$ hw raid. Cost effective and fast, may be not very safe,
but so far so good. All data protection measures from postgresql
are on, of course.
You're aware that many low end SSDs lie to the RAID controller about
having written data, right? Even if the RAID controller sends a
flush command, the SSD might cache the write in non-durable cache.
If you're using such SSDs and you lose power, data corruption is
extremely likely, because your SSDs are essentially ignoring fsync.
Your RAID controller's BBU won't save you, because once the disks
tell the RAID controller the data has hit durable storage, the RAID
controller feels free to flush it from its battery backed cache. If
the disks are lying...
The only solid way to find out if this is an issue with your SSDs is
to do plug-pull testing and find out.
