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 |
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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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