On Mar 8, 2010, at 1:00 AM, Thomas W wrote: > Hi, it's me again. > > First of all, technically slicing the drive worked like it should. > > I started to experiment and found some issues I don't really understand. > > My base playground setup: > - Intel D945GCLF2, 2GB ram, Opensolaris from EON > - 2 Sata Seagates 500GB > > A normal zpool of the two drives to get a TB of space. > Now I added a 1 TB USB drive (I sliced it to have 500GB partitions). I > attached them to the Sata drives to mirror them. > Worked great... > But, suddenly the throughput dropped from around 15MB/s to 300KB/s. After > detaching the USB drives it went back to 15MB/s. > > My Question: > Is it possible that mixing USB 2.0 external drives and Sata drives isn't a > good idea or is the problem that I sliced the external drive? > > After removing the USB drive I done a little benchmarking as I was curious > how well the Intel system works at all. > I wonder if this 'iostat' output is okay (For me it doesn't) > sumpf 804G 124G 257 0 32.0M 0 > sumpf 804G 124G 0 0 0 0 > sumpf 804G 124G 178 0 22.2M 0 > sumpf 804G 124G 78 0 9.85M 0 > sumpf 804G 124G 0 0 0 0 > sumpf 804G 124G 257 0 32.0M 0 > sumpf 804G 124G 0 0 0 0 > sumpf 804G 124G 0 0 0 0 > sumpf 804G 124G 257 0 32.0M 0 > sumpf 804G 124G 0 0 0 0 > sumpf 804G 124G 257 0 32.0M 0 > sumpf 804G 124G 0 0 0 0 > > Why are there so many 0 in this chart? No wonder I only get 15MB/s max...
The Nyquist-Shannon sampling theorem applies here. If a function x(t) contains no frequencies higher than 0.033 Hz, it is completely determined by giving its ordinates at a series of points spaced 15 seconds apart. In other words, if your iostat samples at a higher rate than the txg commit interval (30 seconds), then you can see periods of time where the disk is idle. If your sampling interval is >> 30 seconds, then you will see a smoother I/O rate. -- richard ZFS storage and performance consulting at http://www.RichardElling.com ZFS training on deduplication, NexentaStor, and NAS performance http://nexenta-atlanta.eventbrite.com (March 16-18, 2010) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
