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Re: SSD + RAID

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Greg Smith <greg(at)2ndquadrant(dot)com>
Cc: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: SSD + RAID
Date: 2010-02-22 14:37:13
Message-ID: 201002221437.o1MEbDJ13005@momjian.us (view raw or flat)
Thread:
Lists: pgsql-performance
Greg Smith wrote:
> Ron Mayer wrote:
> > Bruce Momjian wrote:
> >   
> >> Agreed, thought I thought the problem was that SSDs lie about their
> >> cache flush like SATA drives do, or is there something I am missing?
> >>     
> >
> > There's exactly one case I can find[1] where this century's IDE
> > drives lied more than any other drive with a cache:
> 
> Ron is correct that the problem of mainstream SATA drives accepting the 
> cache flush command but not actually doing anything with it is long gone 
> at this point.  If you have a regular SATA drive, it almost certainly 
> supports proper cache flushing.  And if your whole software/storage 
> stacks understands all that, you should not end up with corrupted data 
> just because there's a volative write cache in there.

OK, but I have a few questions.  Is a write to the drive and a cache
flush command the same?  Which file systems implement both?  I thought a
write to the drive was always assumed to flush it to the platters,
assuming the drive's cache is set to write-through.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com
  PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do
  + If your life is a hard drive, Christ can be your backup. +

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