Re: [Xen-users] Optimizing I/O

[Craig Herring <craigeherring@xxxxxxxxx>]

I've found the biggest issue with virtualization is disk I/O. NIC I/O I 
have not seen much of an issue especially if you are using a GB nic. If 
you are having issues with NIC IO this would indicate you are possibly 
approaching 120MB/sec. Although use separate NICs for your different 
networks or bond them with ALB can help. If you are using NFS or iSCSI 
storage use different NICs than your guest networks. Also a good quality 
switch can assist as well, even sometimes overlooked. A good quality HP 
1800 series switch isn't expensive at all. I've seen some tests that 
suggest Intel NICs have less latency, almost half, than most others.
In most situations I find running a RAID 1 / RAID 10 and using less than 
5 VMs per partition is a good rule of thumb to stay away from disk 
contention issues. Also using iSCSI and DRBD can assist in speed as this 
would dedicate a server to handling disk IO. These services can also use 
much of the ram as cache. Stay away from the *fake* RAID stuff or even 
the cheap RAID controllers. Buy the better later gen 3WARE, LSI, Areca 
controllers or just use software RAID. Also format the partition XFS and 
set the noatime flag. The WD RE3/2/Raptor drives are incredibly fast 
especially in a RAID 1.
-Craig

lists@xxxxxxxxxxxx wrote:
> My question was really meant to ask about I/O, in as far as file transferring between main host and network for host and guests but anything is good. 
>
> Just trying to pull all my questions and notes together so that I can get on 
> this in a week or two and it's good to see folks sharing their ideas, methods 
> etc.
>
> So for example, on a system that's pretty much RPM based, what tweaks can 
> someone make to the various configurations files which would greatly help 
> overall network I/O.
>
> Mike
>
>
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