On Mon, Jul 19, 2010 at 01:34:58AM -0700, Garrett D'Amore wrote: ...snip... > > Very simple. 2vdevs gives 2 active "spindles", so you get about twice > the performance of a single disk. > > raidz2 generally gives the performance of a single disk. > > For high performance, if you can sacrifice the storage, I recommend a > vdev made up of two-drive mirrors. This gives pretty good resilience, > and good performance. (Its not as "safe" as say raidz2, though, because > with raidz2 you can lose two drives per vdev, where as with mirrors, you > have many more vdevs and can only lose one drive.) > > With those same 14 drives, you can get 7x the performance instead of 2x > the performance by using mirrors instead of raidz2. > > -- Garrett
I frequently see things like this stated but it doesn't seem like the whole story. A single raidz vdev may limit the IOPS but it can get fairly good throughput with linear access. For instance a single raidz3 vdev of 16 HD203WI Samsung drives (which would then have 13 disks worth of striping) can write linearly with a dd process at easily over 700 MB/s, which, while not being the speed of 13 disks (each disk alone can do about 100 MB/s), is much better than a single disk, and actually the speed of about 7 disks in this case. I would venture to guess that most home servers have little need for lots of random I/O from many clients simultaneously and don't need the high IOPS of several mirrors over one or two vdevs, and such cases might be better served by the safety of raidz2/3 where you have more flexibility in which disks are allowed to fail... Chad _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
