Bottim line with virtual machines is that your IO will be random by
definition since it all goes into the same pipe. If you want to be
able to scale, go with RAID 1 vdevs. And don't skimp on the memory.
Our current experience hasn't shown a need for an SSD for the ZIL but
it might be useful for L2ARC (using iSCSI for VMs, NFS for templates
and iso images)
Cordialement,
Erik Ableson
+33.6.80.83.58.28
Envoyé depuis mon iPhone
On 24 juin 2009, at 18:56, milosz <mew...@gmail.com> wrote:
Within the thread there are instructions for using iometer to load
test your storage. You should test out your solution before going
live, and compare what you get with what you need. Just because
striping 3 mirrors *will* give you more performance than raidz2
doesn't always mean that is the best solution. Choose the best
solution for your use case.
multiple vm disks that have any kind of load on them will bury a raidz
or raidz2. out of a 6x raidz2 you are going to get the iops and
random seek latency of a single drive (realistically the random seek
will probably be slightly worse, actually). how could that be
adequate for a virtual machine backend? if you set up a raidz2 with
6x15k drives, for the majority of use cases, you are pretty much
throwing your money away. you are going to roll your own san, buy a
bunch of 15k drives, use 2-3u of rackspace and four (or more)
switchports, and what you're getting out of it is essentially a 500gb
15k drive with a high mttdl and a really huge theoretical transfer
speed for sequential operations (which you won't be able to saturate
anyway because you're delivering over gige)? for this particular
setup i can't really think of a situation where that would make sense.
Regarding ZIL usage, from what I have read you will only see
benefits if you are using NFS backed storage, but that it can be
significant.
link?
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