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Re: [Xen-users] Optimizing I/O

To: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Optimizing I/O
From: Craig Herring <craigeherring@xxxxxxxxx>
Date: Fri, 23 Jan 2009 00:03:59 -0500
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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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