Scott Roberts <[EMAIL PROTECTED]> writes: > I've been reading through the documentation on ZFS, and was hoping I > could get some clarification and make sure I'm reading everything > right. > > I'm looking to build a NAS box, using sata drives in a double parity > configuration (i.e. raidz2). This is mainly for warehousing large > video files, so access speed and IOPS aren't terribly critical. I > won't immediately need all 15 drives online, so what I would like to > do is be able to resize the raid array. > > Is there any way to resize with ZFS? Or would the only way to do > this be to make one raidz2 with 7 drives, and then when I need to > expand make another raidz2 in the same pool. Obviously having two > virtual devices in the pool means losing 4 drives to parity instead > of just two. > > ie start out with > zpool create tank raidz2 c1t1d0 c1t2d0 c1t3d0 c1t4d0 c2t1d0 c2t2d0 c2t3d0 > > and when i'm ready to expand use > zpool add tank raidz2 c2t4d0 c3t1d0 c3t2d0 c3t3d0 c3t4d0 c4t1d0 c4t2d0 > c4t3d0
I wasn't clear on this myself until earlier this week. I *think* I understand it now, so let me try, and people here can correct me if necessary. You can't add drives to an existing RAIDZ. You can add drives to an existing mirror, but they don't add space, they add reliability. What you *can* do is add additional "things" to your pool, and the space on them becomes available to all filesystems and such drawing from that pool. So yes, you can do what the second thing you describe. The reliability of the pool becomes the reliability of the least-reliable thing in it; so if you have a pool with a RAIDZ in it, and then you add a single drive, everything works and the extra space is available and is used -- and if the single drive fails, you lose data. What you're proposing, adding a second RAIDZ, is fine, and doesn't compromise reliability. It does, as you say, take up another whole parity disk (or two in your raidz2 case). And requires add-ons to be in units bigger than just one drive. -- David Dyer-Bennet, <mailto:[EMAIL PROTECTED]>, <http://www.dd-b.net/dd-b/> RKBA: <http://www.dd-b.net/carry/> Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/> Dragaera/Steven Brust: <http://dragaera.info/> _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
