On Sat, 15 Mar 2008, Richard Elling wrote: > > My observation, is that each metaslab is, by default, 1 MByte in size. Each > top-level vdev is allocated by metaslabs. ZFS tries to allocate a top-level > vdev's metaslab before moving onto another one. So you should see eight > 128kByte allocs per top-level vdev before the next top-level vdev is > allocated. > > That said, the actual iops are sent in parallel. So it is not unusual to see > many, most, or all of the top-level vdevs concurrently busy. > > Does this match your experience?
I do see that all the devices are quite evenly busy. There is no doubt that the load balancing is quite good. The main question is if there is any actual "striping" going on (breaking the data into smaller chunks), or if the algorithm is simply load balancing. Striping trades IOPS for bandwidth. Using my application, I did some tests today. The application was used to do balanced read/write of about 500GB of data in some tens of thousand of reasonably large files. The application sequentially reads a file, then sequentially writes a file. Several copies (2-6) of the application were run at once for concurrency. What I noticed is that with hardly any CPU being used, the read+write bandwidth seemed to be bottlenecked at about 280MB/second with 'zfs iostat' showing very balanced I/O between the reads and the writes. The system I set up is performing quite a bit differently than I anticipated. The I/O is bottlenecked and I find that my application can do significant processing of the data without significantly increasing the application run time. So CPU time is almost free. If I was to assign a smaller block size for the filesystem, would that provide more of the benefits of striping or would it be detrimental to performance due to the number of I/Os? Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
