tsuraan wrote:
> I have a file server with 8 SATA drives formatted with ZFS RAIDZ2. I'm
> using Linux as the host because it's the only OS that I can find that
> properly handled the jmicron controller on the motherboard. Under
> Linux, I can get raw write speeds of 105MB/s to each of the 8 hard
> drives simultaneously. Using the linux zfs implementation
> (zfs-on-fuse), I can get reads of 100MB/s and writes of 250MB/s.
> That's not bad, but it's pretty bad compared with the raw capability
> of the drives,
Welcome to the world of RAID and fuse based file systems.
> so I thought I'd try OpenSolaris under VirtualBox.
You don't expect a guest to go faster than the host, are you??
> I set up the virtual image using a virtual SCSI controller, mapping
> each of the raw drives to SCSI IDs 0-6 and 8 (a drive with ID 7 is
> never seen by OpenSolaris). I did a zfs import to bring the pool
> online, and I ran a simple dd test. My write and read speeds are under
> 30 MB/s.
Welcome to virtualization. If performance is an issue, you shouldn't be
virtualizing. I think you're doing reasonably well at 1/3 of host
performance.
The only VM with reasonable disk I/O performance I've found is KVM. I
did a basic test with XP guest load times (fresh, bare install on each
VM), 4GB RAM host 1GB guest (so the entirety of what is accessed at
startup stick in host's cache). The first time they start they'll hit
all the files in the image required to start, and the second time it'll
all come from the host's cache. Thus, the 2nd pass should give a
reasonable indication of relative overheads of the VM's disk I/O
performance. On the 2nd startup, times to login screen:
VMware Player/Workstation: 40s
VirtualBox: 20s
KVM: 6s (yes, that's six seconds, not a typo)
I haven't been able to get an comparable result for a bare metal XP
because caches in that case don't survive a reboot.
Now, I know this isn't exactly a thorough test, but it is at least
indicative.
> I've tried using the virtual SATA controller (from VirtualBox
> bin), but it just freezes after about 100MB of data written, so I
> can't get a good assessment of the performance there. Can anybody
> recommend any performance tips for IO, give any ideas of what to look
> for, etc?
A virtualized solution will always go slower than the underlying host.
Gordan
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