On Mon, May 10, 2010 at 8:30 PM, Josh Berkus <josh@xxxxxxxxxxxx> wrote: > Ivan, > >> Other things could have influenced your result - 260 MB/s vs 300 MB/s is >> close enough to be influenced by data position on (some of) the drives. >> (I'm not saying anything about the original question.) > > You misread my post. It's *87mb/s* vs. 300mb/s. I kinda doubt that's > position on the drive. That still is consistent with it being caused by the files being discontiguous. Copying them moved all the blocks to be contiguous and sequential on disk and might have had the same effect even if you had left the settings at 8kB blocks. You described it as "overloading the array/drives with commands" which is probably accurate but sounds less exotic if you say "the files were fragmented causing lots of seeks so our drives we saturated the drives' iops capacity". How many iops were you doing before and after anyways? That said that doesn't change very much. The point remains that with 8kB blocks ZFS is susceptible to files becoming discontinuous and sequential i/o performing poorly whereas with 128kB blocks hopefully that would happen less. Of course with 128kB blocks updates become a whole lot more expensive too. -- greg -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
