[libvirt-users] Performance tuning questions for mail server

[Emmanuel Noobadmin]

On 10/7/11, Alex <mysqlstudent at gmail.com> wrote:
> The only thing I haven't done from above is to use ionice on mail
> processes. I'm using RAID5 across three 1TB SATA3 disks,

RAID 5 is another major bottleneck there. The commonly cited write
penalty for RAID 5 appears to be 4 IOPS, while RAID 1/10 is 2 IOPS.
Due to the typical load on an email server with more writes than read,
this become rather punishing.

So you might see a major improvement simply by adding another 1TB and
going for RAID 10.

Personally because of that, as well as the headache of recovering from
a RAID 5 disaster, I've stopped using RAID 5 especially since the cost
of drives are really cheap.

> I'm using
> deadline scheduler, the /var partition is mounted noatime, and the
> disk is mounted raw:
>
>     <disk type='file' device='disk'>
>       <driver name='qemu' type='raw'/>
>       <source file='/var/lib/libvirt/images/mail02.img'/>
>       <target dev='vda' bus='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
> function='0x0'/>

I meant raw disk devices rather than files e.g.
<disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/dev/server02_vg1_2tb/lv_vm03_swap'/>
      <target dev='vdb' bus='virtio'/>
</disk>

This eliminates one layer of filesystem overheads.

> How do I configure BIND to ignore TTLs and keep everything for five
> minutes, as suggested?

I'm not too sure about this sorry.