Re: SSD + RAID

Ron Mayer wrote:
> Bruce Momjian wrote:
> > Greg Smith wrote:
> >> Bruce Momjian wrote:
> >>> I have added documentation about the ATAPI drive flush command, and the
> >>
> >> If one of us goes back into that section one day to edit again it might
> >> be worth mentioning that FLUSH CACHE EXT is the actual ATAPI-6 command
> >> that a drive needs to support properly.  I wouldn't bother with another
> >> doc edit commit just for that specific part though, pretty obscure.
> >
> > That setting name was not easy to find so I added it to the
> > documentation.
>
> If we're spelling out specific IDE commands, it might be worth
> noting that the corresponding SCSI command is "SYNCHRONIZE CACHE"[1].
>
>
> Linux apparently sends FLUSH_CACHE commands to IDE drives in the
> exact sample places it sends SYNCHRONIZE CACHE commands to SCSI
> drives[2].
>
> It seems that the same file systems, SW raid layers,
> virtualization platforms, and kernels that have a problem
> sending FLUSH CACHE commands to SATA drives have he same exact
> same problems sending SYNCHRONIZE CACHE commands to SCSI drives.
> With the exact same effect of not getting writes all the way
> through disk caches.

I always assumed SCSI disks had a write-through cache and therefore
didn't need a drive cache flush comment.

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  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
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