Hi,
Will the upcoming zfs boot capabilities also enable write cache on a
boot disk
like it does on regular data disks (when whole disks are used) ?
//Par
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Pär Känsälä
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Unfortunately not. Thanks, George Par Kansala wrote:> Hi, > > Will the upcoming zfs boot capabilities also enable write cache on a > boot disk > like it does on regular data disks (when whole disks are used) ? > > //Par > -- > -- > <http://www.sun.com> *P?r K?ns?l?* > OEM Engagement Architect > *Sun Microsystems* > Phone +46 8 631 1782 (x45782) > Mobile +46 70 261 1782 > Fax +46 455 37 92 05 > Email Par.Kansala at sun.com > <http://www.sun.com> > > ------------------------------------------------------------------------ > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
Just to clarify a bit, ZFS will not enable the write cache for the root pool. That said, there are disk drives which have the write cache enabled by default. That behavior remains unchanged. - George George Wilson wrote:> Unfortunately not. > > Thanks, > George > > Par Kansala wrote: > >> Hi, >> >> Will the upcoming zfs boot capabilities also enable write cache on a >> boot disk >> like it does on regular data disks (when whole disks are used) ? >> >> //Par >> -- >> -- >> <http://www.sun.com> *P?r K?ns?l?* >> OEM Engagement Architect >> *Sun Microsystems* >> Phone +46 8 631 1782 (x45782) >> Mobile +46 70 261 1782 >> Fax +46 455 37 92 05 >> Email Par.Kansala at sun.com >> <http://www.sun.com> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> zfs-discuss mailing list >> zfs-discuss at opensolaris.org >> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >> >> > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
What is the reasoning behind ZFS not enabling the write cache for the root pool? Is there a way of forcing ZFS to enable the write cache? Thanks Andrew. This message posted from opensolaris.org
Robert Milkowski
2008-Apr-25 14:22 UTC
[zfs-discuss] zfs write cache enable on boot disks ?
Hello andrew,
Thursday, April 24, 2008, 11:03:48 AM, you wrote:
a> What is the reasoning behind ZFS not enabling the write cache for
a> the root pool? Is there a way of forcing ZFS to enable the write cache?
The reason is that EFI labels are not supported for booting.
So from ZFS perspective you put root pool on a slice on SMI labeled
disk - the way currently ZFS works it assumes in such a case that
there could be other slices used by other programs and because you can
enable/disable write cache per disk and not per slice it''s just safer
to not automatically enable it.
If you havoever enable it yourself then it should stay that way (see
format -e -> cache)
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Best regards,
Robert Milkowski mailto:milek at task.gda.pl
http://milek.blogspot.com
> Hello andrew, > > Thursday, April 24, 2008, 11:03:48 AM, you wrote: > > a> What is the reasoning behind ZFS not enabling the > write cache for > a> the root pool? Is there a way of forcing ZFS to > enable the write cache? > > The reason is that EFI labels are not supported for > booting.IIRC that is limited by BIOS, right? I thought the original problem is some x86 BIOS doesn''t understand EFI so they cannot boot. Is there something else prevents from ZFS using EFI labeled disks for boot device? And for the coming zfs root support in new installer, will new installer still create a zfs in a slice rather than the whole device? Now that''s somehow disheartening if we still stuck with SMI and slices. ok, I know write-cache can be forced on with format. I also know that practically EFI doesn''t bring additional advantage over SMI label for small systems. But still...> So from ZFS perspective you put root pool on a slice > on SMI labeled > disk - the way currently ZFS works it assumes in such > a case that > there could be other slices used by other programs > and because you can > enable/disable write cache per disk and not per slice > it''s just safer > to not automatically enable it. > > If you havoever enable it yourself then it should > stay that way (see > format -e -> cache) > > > > -- > Best regards, > Robert Milkowski > mailto:milek at task.gda.pl > http://milek.blogspot.com > _____________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discu > ssThis message posted from opensolaris.org
On Fri, Apr 25, 2008 at 9:22 AM, Robert Milkowski <milek at task.gda.pl> wrote:> Hello andrew, > > Thursday, April 24, 2008, 11:03:48 AM, you wrote: > > a> What is the reasoning behind ZFS not enabling the write cache for > a> the root pool? Is there a way of forcing ZFS to enable the write cache? > > The reason is that EFI labels are not supported for booting. > So from ZFS perspective you put root pool on a slice on SMI labeled > disk - the way currently ZFS works it assumes in such a case that > there could be other slices used by other programs and because you can > enable/disable write cache per disk and not per slice it''s just safer > to not automatically enable it. > > If you havoever enable it yourself then it should stay that way (see > format -e -> cache)So long as the zpool uses all of the space used for dynamic data that needs to survive a reboot, it would seem to make a lot of sense to enable write cache on such disks. This assumes that ZFS does the flush no matter whether it thinks the write cache is enabled or not. Am I wrong about this somehow? -- Mike Gerdts http://mgerdts.blogspot.com/