To tell the truth, I expected zvols to be faster than filesystem datasets. They seem to have less overhead without inodes, posix, acls and so on. So I'm puzzled by test results.
I'm now considering the dd i/o block size, and it means a lot indeed, especially if compared to zvol results with small blocks like 64k. I ran a number of tests with a zvol recreated by commands before each run (this may however cause varying fragmentation impacting results of different runs): # zfs destroy -r pond/test; zfs create -V 30G pond/test; zfs set compression=off pond/test; sync; dd if=/dev/zero of=/dev/zvol/rdsk/pond/test count=1000 bs=512; sync and tests going like # time dd if=/dev/zero of=/dev/zvol/rdsk/pond/test count=1024 bs=1048576 1024+0 records in 1024+0 records out real 0m42.442s user 0m0.006s sys 0m4.292s The test progresses were quite jumpy (with "zpool iostat pond 1" values varying from 30 to 70 MBps, reads coming in sometimes). So I'd stick to overall result - the rounded wallclock time it takes to write 1024 records of varying size and resulting average end-user MBps. I also write "sys" time since that's what is consumed by the kernel and the disk subsystem, after all. I don't write zpool iostat speeds, since they vary too much and I don't bother with a spreadsheen right now. But the reported values stay about halfway between "wallclock MBps" ans "sys MBps" calculations, on the perceived average, peaking at about 350MBps for large block sizes (>4MB). 1 MB (bs=1048576): 42s (4s), 24MBps 4 MB (bs=4194304): 42s (15s), 96MBps 16MB (bs=16777216): 129s-148s (62-64s), 127-110MBps 32MB (bs=33554432, 40Gb zvol): 303s (127s), 108MBps Similar results for writing a file to a filesystem; "zpool iostat" values again jumped anywhere between single MBps to GBps. Simple cleanups used like: # rm /pool/test30g; sync; time dd if=/dev/zero of=/pool/test30g count=1024 bs=33554432 Values remain somewhat consistent (in the same league, at least): 1 MB (bs=1048576, 10240 blocks): 20-21s (7-8s), 512-487MBps 1 MB (bs=1048576): 2.3s (0.6s), 445MBps 4 MB (bs=4194304): 8s (3s), 512MBps 16MB (bs=16777216): 37s (15s), 442MBps 32MB (bs=33554432): 74-103s (32-42s), 442-318MBps 64Kb (bs=65536, 545664 blocks): 94s (47s), 362MBps All in all, to make more precise results these tests should be made in greater numbers and averaged. But here we got some figures to think about... On a side note, now I'll pay more attention to tuning suggestions which involve multi-megabyte buffers for network sockets, etc. They can actually cause an impact to performance many times over! On another note, For some reason I occasionally got results like this: write: File too large 1+0 records in 1+0 records out I think the zvol was not considered created by that time. In about 10-15 sec I was able to commence the test run. Perhaps it helped that I "initialized" the zvol by a small write after creation, then: # dd if=/dev/zero of=/dev/zvol/rdsk/pond/test count=1000 bs=512 Strange... -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
