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I know that first release of ZFS boot will be support single disk and
mirroring configurations. With ZFS "copies" support in Solaris 10 U5
(I
hope), I was wondering about breaking my current mirror and using both
disks in stripe mode, protecting the critical bits with ZFS "copies" .
Those bits would include the OS.
Would ZFS boot be able to boot from a "copies" boot dataset, when one
of
the disks are failing?. Counting that ditto blocks are spread between
both disks, of course.
PS: ZFS "copies" = Ditto blocks.
- --
Jesus Cea Avion _/_/ _/_/_/ _/_/_/
jcea at argo.es http://www.argo.es/~jcea/ _/_/ _/_/ _/_/ _/_/ _/_/
jabber / xmpp:jcea at jabber.org _/_/ _/_/ _/_/_/_/_/
_/_/ _/_/ _/_/ _/_/ _/_/
"Things are not so easy" _/_/ _/_/ _/_/ _/_/ _/_/ _/_/
"My name is Dump, Core Dump" _/_/_/ _/_/_/ _/_/ _/_/
"El amor es poner tu felicidad en la felicidad de otro" - Leibniz
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Jesus Cea wrote:> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > I know that first release of ZFS boot will be support single disk and > mirroring configurations. With ZFS "copies" support in Solaris 10 U5 (I > hope), I was wondering about breaking my current mirror and using both > disks in stripe mode, protecting the critical bits with ZFS "copies" . > Those bits would include the OS.Why would you do that when it would reduce your protection and ZFS boot can boot from a mirror anyway. What problem are you trying to solve ? The only thing I can think of is attempting to increase performance by increasing the number of spindles. -- Darren J Moffat
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Darren J Moffat wrote:> Why would you do that when it would reduce your protection and ZFS boot > can boot from a mirror anyway.I guess ditto blocks would be protection enough, since the data would be duplicated between both disks. Of course, backups are your friend.> What problem are you trying to solve ? The only thing I can think of is > attempting to increase performance by increasing the number of spindles.Read performance would double, and this is very nice, but my main motivation would be disk space: I have some hundred of gigabytes of data that I could easily recover from a backup, or that I wouldn''t mind to lose if something catastrofic enough occurs. For example, divx movies or MP3''s files. Since I do daily backups, selective ZFS "copies" could almost double my diskspace. I don''t need to mirror my "/usr/local/" if I have daily backups. But I could protect the boot environment or my mail dataset using ditto blocks. Playing with ZFS "copies", I can use a single pool and modulate space/protection per dataset according to my needs and compromises. - -- Jesus Cea Avion _/_/ _/_/_/ _/_/_/ jcea at argo.es http://www.argo.es/~jcea/ _/_/ _/_/ _/_/ _/_/ _/_/ jabber / xmpp:jcea at jabber.org _/_/ _/_/ _/_/_/_/_/ _/_/ _/_/ _/_/ _/_/ _/_/ "Things are not so easy" _/_/ _/_/ _/_/ _/_/ _/_/ _/_/ "My name is Dump, Core Dump" _/_/_/ _/_/_/ _/_/ _/_/ "El amor es poner tu felicidad en la felicidad de otro" - Leibniz -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iQCVAwUBRwObzZlgi5GaxT1NAQJq7gP/V1g6KUPS8T9hnA3KDmKMbIeDKoqphRO5 POehmhnWsPlO8BPa+CxT/ZRUwbNYCte9kYYWeJzXNRpUyGtFvREBjtgK6swIQXUC n0D0gG0yI4aU1qzdX8X4bqomDaoL/Ho7YQu00j+P8mEfUdYzqY/odOVklZKq92U3 zfyDj7fgTVQ=cDSg -----END PGP SIGNATURE-----
Jesus Cea wrote:> Darren J Moffat wrote: > > Why would you do that when it would reduce your protection > and ZFS boot > > can boot from a mirror anyway. > > I guess ditto blocks would be protection enough, since the > data would be > duplicated between both disks. Of course, backups are your friend.I asked almost the exact same question when I first heard about ditto blocks. (See http://mail.opensolaris.org/pipermail/zfs-discuss/2007-May/040596.html and followups) There are 2 key differences between ditto blocks and mirrors: 1) The ZFS pool is considered "unprotected". That means a device failure will result in a kernel panic. 2) Ditto block separation is not enforced. The allocator tries to keep the second copy "far" from the first one, but it is possible that both copies of your /etc/passwd file are on the same VDEV. This means that a device failure could result in real loss of data. It would be really nice if there was some sort of enforced-ditto-separation (fail w/ device full if unable to satisfy) but that doesn''t exist currently. --Joe
Moore, Joe wrote:> It would be really nice if there was some sort of > enforced-ditto-separation (fail w/ device full if unable to satisfy) but > that doesn''t exist currently.How would that be different to a mirror ? I guess it is different to a mirror because only some datasets in the pool would be "mirrored" instead of all of them. -- Darren J Moffat
Jesus Cea wrote:> Read performance [when using "zfs set copies=2" vs a mirror] would double, and this is very niceI don''t see how that could be the case. Either way, the reads should be able to fan out over the two disks. --matt
Jesus Cea wrote:> Would ZFS boot be able to boot from a "copies" boot dataset, when one of > the disks are failing?. Counting that ditto blocks are spread between > both disks, of course.You can not boot from a pool with multiple top-level vdevs (eg, the "copies" pool you describe). We hope to enhance zfs boot to provide this functionality at a later date. --matt