Write Performance issues: zvols and XEN

[tentonwire]

I've been doing some simple benchmarking for I/O, and I've run into some write performance problems.

Using debian-patched 2.6.32-30 kernel and xen 4.0.1-2 for the xenified tests.

Test is timing dding a 10GB image file.stored on another hard drive not in the zpool (but attached to the same sata controller, but that shouldn't bottleneck it) to the zfs file system or zvols.

zpool is raidz of 3 hard drives. For reference, writing straight to the hard disk is 110 MB/s. All numbers in the table are in MB/s.

Write:	to file	to zvol
Solaris 11 Express xVM (Xen 3.2)	75	75
Vanilla Linux with zfs-linux	100	20
Xenified Kernel with zfs-linux	14	8

So first of all, zvols have a huge write hit. In addition, all performance in XEN is very slow. In fact, it appears as though the xen kernel suffers the same hit as a vanilla linux zvol with an additional hit from xen overhead.

Hopefully this is considered a high priority, as many people interested in zfs-linux are people migrating away from opensolaris + xVM + crossbow, which is arguably the best virtualization platform.

[nkhare]

Thank you doing the benchmarking and sharing the numbers.

We are aware of zvol performance issue. Some other users also reported it.
We are treating this as high priority issue and should be able fix it soon.