[libvirt-users] Performance tuning questions for mail server

[Alex]

Hi,

>> This mail server does manage a lot of mail per day, but not enough to
>> even consume the 8GB I've allocated, and the "mailq" command typically
>> takes a few seconds to respond, even when there's only a few messages
>> in the queue.
>>
>> iotop may report as much as 2M/s on the host, with an average of about
>> 400-600K/s. Does that seem like a lot? I can write like 80MB/s at
>> least using dd to test.
>
> I had similar problems previously. The crux in my case is the number
> of IOPS possible. 100K of 2KB file writes is still 2MB/s but requires
> a lot more IO overheads than 1 single 2MB file.
>
> Recommendations that I was given which stopped the system from locking
> up included
> 1. use ionice on the mail process
> 2. change the IO scheduler/elevator from the default CFQ
> 3. switch from file-based virtual drives to raw disk devices
> 4. mount filesystems with noatime
>
> Also, are you using RAID 5?

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, 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'/>

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

Thanks,
Alex