Hi Steve, Am 24.05.2008 um 10:17 schrieb [EMAIL PROTECTED]: > ZFS: A general question > To: zfs-discuss@opensolaris.org > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=UTF-8 > > Hello everyone, > > I'm new to ZFS and OpenSolaris, and I've been reading the docs on > ZFS (the pdf "The Last Word on Filesystems" and wikipedia of > course), and I'm trying to understand something. > > So ZFS is self-healing, correct? This is accomplished via parity > and/or metadata of some sort on the disk, right? So it protects > against data corruption, but not against disk failure. This is not entirely true, but possible. You can use the copies attribute to have some sort of redundancy on a single disk. But obviously, if yo only use a single disk and it breaks completely, data loss can not be avoided. Even without redundancy features ZFS, provides very good detection of block failure and snapshots that can be used to avoid accidental deletion/unwanted changes of data > Or is it the case that ZFS intelligently puts the parity and/or > metadata on alternate disks to protect against disk failure, even > without a raid array? You do not need a hardware RAID array to get these features and you can theoretically even use partitions/slices on a single disk, but to get good protection and acceptable performance, you will need multiple drives, since a drive can always fail in a way that it is completely unusable (i.e. it does not spin up anymore). > > Anyway you can add mirrored, striped, raidz, or raidz2 arrays to the > pool, right? But you can't "effortlessly" grow/shrink this > protected array if you wanted to add a disk or two to increase your > protected storage capacity. A number of redundant disks is called vdev - this is probably what you call "array". A vdev can be build from disks, files, iscsi targets or partitions. Several vdevs form a storage pool. You can increase the size of a pool by adding extra vdevs or replacing all members of a vdev with bigger ones. > My understanding is that if you want to add storage to a raid array, > you must copy all your data off the array, destroy the array, > recreate it with your extra disk(s), then copy all your data back. This is currently true for shrinking a pool and for changing the number of devices in a raidz1/2 vdev. Some efforts have been made to change that - see
http://blogs.sun.com/ahl/entry/expand_o_matic_raid_z Theoretically it should also be possible to "evacuate" vdevs (and remove them from a pool), but I do not think any code has been written to do so. The main reason is that Sun's paying customers are probably reasonably happy to just add a vdev to increase storage, so other features are much higher on their priority list. > > I like the idea of a protected storage pool that can grow and shrink > effortlessly, but if protecting your data against drive failure is > not as effortless, then honestly, what's the point? In my opinion, > the ease of use should be nearly that of the Drobo product. Which > brings me to my final question: is there a gui tool available? I > can use command line just like the next guy, but gui's sure are > convenient... I'd say: The point is "First things first". Sun provides a free, reasonably manageable very robust storage concept that does not have all desirable features (yet). For a nice GUI-Tool you might have to wait for Mac OS X 10.6 ;-) Hope this helps, ralf _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
