Hi, > How are paired mirrors more flexiable?
well, I'm talking of a small home system. If the pool gets full, the way to expand with RAID-Z would be to add 3+ disks (typically 4-5). With mirror only, you just add two. So in my case it's just about the granularity of expansion. The reasoning is that of the three factors reliability, performance and space, I value them in this order. Space comes last since disk space is cheap. If I had a bigger number of disks (12+), I'd be using them in RAID-Z2 sets (4+2 plus 4+2 etc.). Here, the speed is ok and the reliability is ok and so I can use RAID-Z2 instead of mirroring to get some extra space as well. > Right now, i have a 3 disk raid 5 running with the linux DM driver. One > of the most resent additions was raid5 expansion, so i could pop in a > matching disk, and expand my raid5 to 4 disks instead of 3 (which is > always interesting as your cutting on your parity loss). I think though > in raid5 you shouldn't put more then 6 - 8 disks afaik, so I wouldn't be > expanding this enlessly. > > So how would this translate to ZFS? I have learned so far that, ZFS ZFS does not yet support rearranging the disk cofiguration. Right now, you can expand a single disk to a mirror or an n-way mirror to an n+1 way mirror. RAID-Z vdevs can't be changed right now. But you can add more disks to a pool by adding more vdevs (You have a 1+1 mirror, add another 1+1 pair and get more space, have a 3+2 RAID-Z2 and add another 5+2 RAID etc.) > basically is raid + LVM. e.g. the mirrored raid-z pairs go into the > pool, just like one would use LVM to bind all the raid pairs. The > difference being I suppose, that you can't use a zfs mirror/raid-z > without having a pool to use it from? Here's the basic idea: - You first construct vdevs from disks: One disk can be one vdev. A 1+1 mirror can be a vdev, too. A n+1 or n+2 RAID-Z (RAID-Z2) set can be a vdev too. - Then you concatenate vdevs to create a pool. Pools can be extended by adding more vdevs. - Then you create ZFS file systems that draw their block usage from the resources supplied by the pool. Very flexible. > Wondering now is if I can simply add a new disk to my raid-z and have it > 'just work', e.g. the raid-z would be expanded to use the new > disk(partition of matching size) If you have a RAID-Z based pool in ZFS, you can add another group of disks that are organized in a RAID-Z manner (a vdev) to expand the storage capacity of the pool. Hope this clarifies things a bit. And yes, please check out the admin guide and the other collateral available on ZFS. It's full of new concepts and one needs some getting used to to explore all possibilities. Cheers, Constantin -- Constantin Gonzalez Sun Microsystems GmbH, Germany Platform Technology Group, Global Systems Engineering http://www.sun.de/ Tel.: +49 89/4 60 08-25 91 http://blogs.sun.com/constantin/ Sitz d. Ges.: Sun Microsystems GmbH, Sonnenallee 1, 85551 Kirchheim-Heimstetten Amtsgericht Muenchen: HRB 161028 Geschaeftsfuehrer: Marcel Schneider, Wolfgang Engels, Dr. Roland Boemer Vorsitzender des Aufsichtsrates: Martin Haering _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
