I am asssuming you will put all of the vdevs into a single pool, which is a good idea unless you have a specific reason for keeping them separate, e.g. you want to be able to destroy / rebuild a particular vdev while leaving the others intact.
Fewer disks per vdev implies more vdevs, providing better random performance, lower scrub and resilver times and the ability to expand a vdev by replacing only the few disks in it. The downside of more vdevs is that you dedicate your parity to each vdev, e.g. a RAIDZ2 would need two parity disks per vdev. > I'm in two minds with mirrors. I know they provide > the best performance and protection, and if this was > a business critical machine I wouldn't hesitate. > > But as it for a home media server, which is mainly > WORM access and will be storing (legal!) DVD/Bluray > rips i'm not so sure I can sacrify the space. For a home media server, all accesses are essentially sequential, so random performance should not be a deciding factor. > 7x 2 way mirrors would give me 7TB usable with 1 hot > spare, using 1TB disks, which is a big drop from > 12TB! I could always jump to 2TB disks giving me 14TB > usable but I already have 6x 1TB disks in my WHS > build which i'd like to re-use. I would be tempted to start with a 4+2 (six disk RAIDZ2) vdev using your current disks and plan from there. There is no reason you should feel compelled to buy more 1TB disks just because you already have some. > Am I right in saying that single disks cannot be > added to a raid-z* vdev so a minimum of 3 would be > required each time. However a mirror is just 2 disks > so if adding disks over a period of time mirrors > would be cheaper each time. That is not correct. You cannot ever add disks to a vdev. Well, you can add additional disks to a mirror vdev, but otherwise, once you set the geometry, a vdev is stuck for life. However, you can add any vdev you want to an existing pool. You can take a pool with a single vdev set up as a 6x RAIDZ2 and add a single disk to that pool. The previous example is a horrible idea because it makes the entire pool dependent upon a single disk. The example also illustrates that you can add any type of vdev to a pool. Most agree it is best to make the pool from vdevs of identical geometry, but that is not enforced by zfs. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
