Hello Peter, Thursday, January 4, 2007, 1:12:47 AM, you wrote:
>> I've been using a simple model for small, random reads. In that model, >> the performance of a raidz[12] set will be approximately equal to a single >> disk. For example, if you have 6 disks, then the performance for the >> 6-disk raidz2 set will be normalized to 1, and the performance of a 3-way >> dynamic stripe of 2-way mirrors will have a normalized performance of 6. >> I'd be very interested to see if your results concur. PS> Is this expected behavior? Assuming concurrent reads (not synchronous and PS> sequential) I would naively expect an ndisk raidz2 pool to have a normalized PS> performance of n for small reads. PS> Is there some reason why a small read on a raidz2 is not statistically very PS> likely to require I/O on only one device? Assuming a non-degraded pool of PS> course. Unfortunately there's. With raid-z1 and raid-z2 there's no free lunch. You get excellent write performance (better than raid-10) however read performance for small IOs will suffer. It's because in case of raid-z[12] each logical file system block is spread to all disks (minus parity disks). So in order to just read one block you have to get data from all disks in a raid-z[12] group. This is not something many people would expect knowing traditional raids. It's not the case with striping and raid-1[0] in zfs. -- Best regards, Robert mailto:[EMAIL PROTECTED] http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
