The amount of disk space is the same but the protection from device failure is
better. Protection probably isn't the right word. Our RAS expert, Richard
Elling, explains this better:
For single parity schemes (2-way mirror, raidz, RAID-1, RAID-5):
MTTDL = MTBF2 / (N * (N-1) * MTTR)
For double parity schemes (3-way mirror, raidz2, RAID-6):
MTTDL = MTBF3 / (N * (N-1) * (N-2) * MTTR2)
>From his blog, here:
http://blogs.sun.com/relling/entry/raid_recommendations_space_vs_mttdl
Cindy
> How much disk space do I have in a 3-way mirror?
> Having three disks of equal space, for me makes
> no sense having three disks mirrored, or do I get
> something
> wrong?
>
> > Hi Andres,
> >
> > For general ZFS best practices info, please see
> this site:
> >
> >
> http://www.solarisinternals.com/wiki/index.php/ZFS_Bes
> t_Practices_Guide
> >
> > For your specific questions, creating a mirrored
> ZFS configuration
> > provides
> > the most flexibility if you want to change the
> device configuration.
> >
> > For example, you could start with a two-way mirror,
> like this:
> >
> > # zpool create tank mirror c1t0d0 c2t0d0
> >
> > Then, attach another disk for a 3-way mirror:
> >
> > # zpool attach tank c2t0d0 c3t0d0
> >
> > If you get more disks, add another 3-way mirror:
> >
> > # zpool add tank mirror c3t0d0 c4t0d0 c5t0d0
> >
> > Even better, add some spares:
> >
> > # zpool add tank spare c2t1d0 c3t1d0
> >
> > If you change you mind, go back to two, 2-way
> mirrors:
> >
> > # zpool detach tank c3t0d0
> > # zpool detach tank c5t0d0
> >
> > If you want to replace the existing disks, with
> larger disks, then:
> >
> > # zpool replace tank c1t0d0 c6t0d0
> >
> > and so on, until all the disks are replaced.
> >
> > Similar examples are available in the ZFS
> Administration Guide:
> >
> >
> http://docs.sun.com/app/docs/doc/817-2271/gavwn?a=view
> >
> > You cannot currently remove a device except to
> replace a disk
> > in a mirrored or RAIDZ configuration, or detach a
> disk in a mirrored
> > configuration.
> >
> > Cindy
> >
> >> Is there any best practice summary for managing
> ZFS
> >> pool, specifically
> >> related to adding/removing/replacing drives or
> >> changing layout?
> >>
> >> On 3/18/08, Andre Lue <[EMAIL PROTECTED]> wrote:
> >> > Yes you have to backup the data and recreate the
> >> pool then restore.
> >> >
> >> >
> >> > This message posted from opensolaris.org
> >> > _______________________________________________
> >> > storage-discuss mailing list
> >> > [email protected]
> >> >
> >>
> http://mail.opensolaris.org/mailman/listinfo/storage-d
> >> iscuss
> >> >
> >>
> >>
> >> --
> >> Regards,
> >> Andrey
> >> _______________________________________________
> >> storage-discuss mailing list
> >> [email protected]
> >>
> http://mail.opensolaris.org/mailman/listinfo/storage-d
> >> iscuss
> >
> >
> > This message posted from opensolaris.org
> > _______________________________________________
> > storage-discuss mailing list
> > [email protected]
> >
> http://mail.opensolaris.org/mailman/listinfo/storage-d
> iscuss
> >
>
>
> _______________________________________________
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> iscuss
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