RE: [Xen-users] Optimizing I/O

["Robert Dunkley" <Robert@xxxxxxxxx>]

Some very good advice below. If you have the budget for a decent san
type box for storage then Infiniband + RDMA + ISCSI + DRBD on two
mirrored boxes should allow for excellent performance and easy failover.


Also, I cannot stress enough the importance of a decent raid card,
spread the VMs across multiple raid 1 arrays and a decent SAS card
should let you mix and match SAS and SATA drive arrays which is often
convenient.

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Rudi Ahlers
Sent: 23 January 2009 12:53
To: Craig Herring
Cc: xen-users
Subject: Re: [Xen-users] Optimizing I/O

If possible, add as many disks to the machine as it can take, and
spread the VM's out across the disks / partitions.

Or, if you can, setup RAID 10 to help load the IO of different data
onto different disks / controllers. Don't use IDE, and try and get the
fastest disks for your budget. SATA II isn't that much more expensive
than IDE. Or if you can afford it, and the mobo can handle it, get
SCSI or SAS drives.

On Fri, Jan 23, 2009 at 7:03 AM, Craig Herring <craigeherring@xxxxxxxxx>
wrote:
> 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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>>
>
>
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>



-- 

Kind Regards
Rudi Ahlers

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