On Wed, Dec 30, 2009 at 9:35 PM, Ross Walker <rswwal...@gmail.com> wrote: > On Dec 30, 2009, at 11:55 PM, "Steffen Plotner" <swplot...@amherst.edu> > wrote: > > Hello, > > I was doing performance testing, validating zvol performance in > particularly, and found that zvol write performance to be slow ~35-44MB/s at > 1MB blocksize writes. I then tested the underlying zfs file system with the > same test and got 121MB/s. Is there any way to fix this? I really would > like to have compatible performance between the zfs filesystem and the zfs > zvols. > > Been there. > ZVOLs were changed a while ago to make each operation synchronous so to > provide data consistency in the event of a system crash or power outage, > particularly when used as backing stores for iscsitgt or comstar. > While I think that the change is necessary I think they should have made the > cooked 'dsk' device node run with caching enabled to provide an alternative > for those willing to take the risk, or modify iscsitgt/comstar to issue a > sync after every write if write-caching is enabled on the backing device and > the user doesn't want to write cache, or advertise WCE on the mode page to > the initiators and let them sync. > I also believe performance can be better. When using zvols with iscsitgt and > comstar I was unable to break 30MB/s with 4k sequential read workload to a > zvol with a 128k recordsize (recommended for sequential IO), not very good. > To the same hardware running Linux and iSCSI Enterprise Target I was able to > drive over 50MB/s with the same workload. This isn't writes, just reads. I > was able to do somewhat better going to the physical device with iscsitgt > and comstar, but not as good as Linux, so I kept on using Linux for iSCSI > and Solaris for NFS which performed better. > -Ross > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > >
I also noticed that using ZVOLS instead of files, for 20MB/sec read I/O, I saw as many as 900 iops to the disks themselves. When using file based luns to Comstar, doing 20MB/sec read I/O will just issue a couple hundred iops. Seemed to get decent performance, it was required for me to either throw away my X4540's and switch to 7000's with expensive SSDs, or switch to file-based Comstar LUNs and disable the ZIL :( Sad when a $50k piece of equipment requires such sacrifice. -- Brent Jones br...@servuhome.net _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
