Re: io performance...

[Bartlomiej Zolnierkiewicz]

On 1/18/06, Phillip Susi <psusi@xxxxxxxxxx> wrote:
> I was going to say, doesn't the kernel set the FUA bit on the write
> request to push important flushes through the disk's write-back cache?
> Like for filesystem journal flushes?

Yes if:
* you have a disk supporting FUA
* you have kernel >= 2.6.16-rc1
* you are using SCSI (this includes libata) driver [ support for IDE driver
  will be merged later when races in changing IDE  settings are fixed ]

Bartlomiej

> Alan Cox wrote:
> > Not always. If you have a cache flush command and the OS knows about
> > using it, or if you don't care if the data gets lost over a power
> > failure (eg /tmp and swap) it makes sense to force it.
> >
> > The raid controller drivers that fake scsi don't always fake enough of
> > scsi to report that they support cache flushes and the like. That
> > doesn't mean the controller itself is neccessarily doing one thing or
> > the other.
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