Re: SSD + RAID

Greg Smith wrote:
> Ron Mayer wrote:
> > Linux apparently sends FLUSH_CACHE commands to IDE drives in the
> > exact sample places it sends SYNCHRONIZE CACHE commands to SCSI
> > drives[2].
> > [2] http://hardware.slashdot.org/comments.pl?sid=149349&cid=12519114
> >
>
> Well, that's old enough to not even be completely right anymore about
> SATA disks and kernels. It's FLUSH_CACHE_EXT that's been added to ATA-6
> to do the right thing on modern drives and that gets used nowadays, and
> that doesn't necessarily do so on most of the SSDs out there; all of
> which Bruce's recent doc additions now talk about correctly.
>
> There's this one specific area we know about that the most popular
> systems tend to get really wrong all the time; that's got the
> appropriate warning now with the right magic keywords that people can
> look into it more if motivated. While it would be nice to get super
> thorough and document everything, I think there's already more docs in
> there than this project would prefer to have to maintain in this area.
>
> Are we going to get into IDE, SATA, SCSI, SAS, FC, and iSCSI? If the
> idea is to be complete that's where this would go. I don't know that
> the documentation needs to address every possible way every possible
> filesystem can be flushed.

The bottom line is that the reason we have so much detailed
documentation about this is that mostly only database folks care about
such issues, so we end up having to research and document this
ourselves --- I don't see any alternatives.

--
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