Re: [Xen-users] Accessing SSD disks on VM

["Fajar A. Nugraha" <list@xxxxxxxxx>]

On Mon, Sep 3, 2012 at 2:54 PM, Lloyd Dizon <thecarrionkind@xxxxxxxxx> wrote:
> Hi,
> Do you have suggestions on how to properly access SSD disks?
> Currently I have a RAID0 on two SSD disks, accessible as /dev/md0.
> md0 is used as a PV with LVM, on which I have a VG and a LV.
> The LV is seen as xvda by the VM. I am using the whole LV as a root
> device for the VM (no partitions).

That works. Although if it's raid0 I'd just use LVM directly without md.

Or, since you seem to only use the SSD for the domU anyway, you can
pass the SSDs (/dev/sd*) to domU, and do LVM there.

>
> I am seeing up to 25% less performance on the VM when doing IO tests
> (not sure if I am doing the correct way to test IO).

Nope :) Your test is basically influenced by cache.

IMHO something like bonnie++ or fio (configured with random r/w) is
better. And make sure your test size is at least twice the RAM.

And there ARE some performance penalty in domU, though I don't know
what the "normal" number is nowadays.

-- 
Fajar

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