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Re: SSD + RAID

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Brad Nicholson <bnichols(at)ca(dot)afilias(dot)info>, Karl Denninger <karl(at)denninger(dot)net>, Laszlo Nagy <gandalf(at)shopzeus(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: SSD + RAID
Date: 2009-11-30 16:40:11
Message-ID: 200911301640.nAUGeBK23759@momjian.us (view raw or flat)
Thread:
Lists: pgsql-performance
Ron Mayer wrote:
> Bruce Momjian wrote:
> > Greg Smith wrote:
> >> Bruce Momjian wrote:
> >>> I thought our only problem was testing the I/O subsystem --- I never
> >>> suspected the file system might lie too.  That email indicates that a
> >>> large percentage of our install base is running on unreliable file
> >>> systems --- why have I not heard about this before?
> >>>   
> >> he reason why it 
> >> doesn't bite more people is that most Linux systems don't turn on write 
> >> barrier support by default, and there's a number of situations that can 
> >> disable barriers even if you did try to enable them.  It's still pretty 
> >> unusual to have a working system with barriers turned on nowadays; I 
> >> really doubt it's "a large percentage of our install base".
> > 
> > Ah, so it is only when write barriers are enabled, and they are not
> > enabled by default --- OK, that makes sense.
> 
> The test program I linked up-thread shows that fsync does nothing
> unless the inode's touched on an out-of-the-box Ubuntu 9.10 using
> ext3 on a straight from Dell system.
> 
> Surely that's a common config, no?

Yea, this certainly suggests that the problem is wide-spread.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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