From: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: SSD + RAID |
Date: | 2010-02-21 14:54:24 |
Message-ID: | 4B814920.1040204@cheapcomplexdevices.com |
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Lists: | pgsql-performance |
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:
Under 120GB Maxtor drives from late 2003 to early 2004.
and it's apparently been worked around for years.
Those drives claimed to support the "FLUSH_CACHE_EXT" feature (IDE
command 0xEA), but did not support sending 48-bit commands which
was needed to send the cache flushing command.
And for that case a workaround for Linux was quickly identified by
checking for *both* the support for 48-bit commands and support for the
flush cache extension[2].
Beyond those 2004 drive + 2003 kernel systems, I think most the rest
of such reports have been various misfeatures in some of Linux's
filesystems (like EXT3 that only wants to send drives cache-flushing
commands when inode change[3]) and linux software raid misfeatures....
...and ISTM those would affect SSDs the same way they'd affect SATA drives.
[1] http://lkml.org/lkml/2004/5/12/132
[2] http://lkml.org/lkml/2004/5/12/200
[3] http://www.mail-archive.com/linux-kernel(at)vger(dot)kernel(dot)org/msg272253.html
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