> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of besson3c > > I'm wondering if somebody can kindly direct me to a sort of newbie way > of assessing whether my ZFS pool performance is a bottleneck that can > be improved upon, and/or whether I ought to invest in a SSD ZIL > mirrored pair? I'm a little confused by what the output of iostat,
There are a few generalities I can state, which may be of use: * If you are serving NFS, then it's likely you're doing sync write operations, and therefore likely that a dedicated zil log device could benefit your write performance. To find out, you can disable your ZIL (requires dismounting & remounting filesystem) temporarily and test performance with the ZIL disabled. If there is anything less than a huge performance gain, then there's no need for a dedicated log device. * If you are doing large sequential read/write, then the performance of striping/mirroring/raidz are all comparable given similar numbers of usable disks. That is, specifically: o If you do a large sequential read, with 3 mirrors (6 disks) then you get 6x performance of a single disk. o If you do a large sequential read, with 7-disk raidz (capacity of 6 disks) then you get 6x performance of a single disk. o If you do a large sequential write, with 3 mirrors (6 disks) then you get 3x performance of a single disk. o If you do a large sequential write, with 7-disk raidz (capacity of 6 disks) then you get 6x performance of a single disk. * So, for large sequential operations, the raidz would be cheaper and probably slightly faster. * If you do small random operations, then striping/mirroring can vastly outperform raidz. Specifically: o If you do random reads, with 3 mirrors (6 disks) then you get 4x-5x performance of a single disk. (Assuming you have multiple threads or processes issuing those reads, or your read requests are queueable in any way.) o If you do random reads, with 7-disk raidz (capacity of 6 disks) you get about 50% faster than a single disk o If you do random writes, with 3 mirrors, then you get about 2x performance of a single disk o If you do random writes, with 7-disk raidz, you get about 50% faster than a single disk * So, for small operations, the striping/mirroring would certainly be faster. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
