Xen project Mailing List

Hi Jonathan,

There is the complicated scripted scientific approach which I did not have time for when I constructed things here although others on the list might be able to help you with that sort of benchamrking.

I just ran Bonnie and timed DD on a couple of Linux VMs whilst running Sandra on couple of Windows VMs and coincide them to roughly finish at the same time. Whichever setup provided decent all round results whilst all were running would be my choice. The scheduler selection in Dom0 also affected disk performance a fair bit.

I also tested the replicated arrays we have using IOZone from Dom 0. I attach my results from one of our systems using a simple raid 1 array of both 7.2K SATA and 15K SAS disks. It will hopefully show you the affect of different raid controller settings on different IO usage scenarios.

Our setup here was storage on the VM servers but replicated between them using DRBD, might sound different to yours but testing is similar.

Testing first on the local arrays and tweaking the raid controller settings and driver along with local IO cache settings would be your first step. Then team up your NICs and use something like iperf to tweak your MTU and other settings for max bandwidth. Then do the same IOZone tests from a Dom0 using ISCSI and try to optimise your ISCSI as best you can. Lastly test from the VM and optimise the Xen config as best you can. Splitting the above tasks will allow you to work on one area at a time and aim any questions you might have at the correct mailing list / forum for each one.

Rob

From: Jonathan Tripathy [mailto:jonnyt@xxxxxxxxxxx]
Sent: 17 June 2010 10:37
To: Robert Dunkley; Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] RAID10 Array

Hi Rob,

Good tip.

Can you suggest a way I could benchmark all these things? I've never benchmarked Hard Drives before..

Thanks

From: Robert Dunkley [mailto:Robert@xxxxxxxxx]
Sent: Thu 17/06/2010 10:06
To: Jonathan Tripathy; Adi Kriegisch; Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] RAID10 Array

Hi,

I like the sound of idea 1 best. One big Raid 10 might sound nice but are you sure it is purely bandwidth you need. For small file latency I think a number of smaller arrays spread between the different VMs might be faster (eg. 4 Raid 10 or 4 Raid 5). Seperate arrays also provides some degree of performance isolation between the LUNs. The Raid 1 part of raid 10 does allow for read interleaving but if you have random mixed reads and writes occurring fairly evenly across the VMs then separate arrays should be more responsive (Even with read and write caching enabled on the raid card).

The way to find out is to benchmark with multiple VMs simultaneously.

Rob

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jonathan Tripathy
Sent: 17 June 2010 09:09
To: Adi Kriegisch; Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] RAID10 Array

From: Adi Kriegisch [mailto:kriegisch@xxxxxxxx]
Sent: Thu 17/06/2010 08:32
To: Jonathan Tripathy
Cc: Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] RAID10 Array

Hi!

> I have 3 RAID ideas, and I'd appreciate some advice on which would be
> better for lots of VMs for customers.
>
> My storage server will be able to hold 16 disks. I am going to export 1
> iSCSI LUN to each xen node. 6 nodes will connect to one storage server,
> so that's 6 LUNs per server of equal size. The server will connect to a
> switch using quad port bonded NICs (802.3ad), and each Xen node will
> connect to the switch using Dual port bonded NICs.
hmmm... with one LUN per server you will loose the ability to do live
migration -- or do I miss something?
Some people mention problems with bonding more than two NICs for iSCSI as
the reordering of the commands/packets adds tremendously to latency and load.
If you want high performance and avoid latency issues you might want to
choose ATA-over-Ethernet.

> I'd appreciate any thoughts or ideas on which would be best for
> throughput/IPOS
Your server is a Linux box exporting the RAIDs to your Xen servers? Then
just take fio and do some benchmarking. If you're using software raid than
you might want to add RAID5 to the equation.
I'd suggest to measure performance of your RAID system with various
configurations and then choose which level of isolation gives the best
performance.
I don't think a setup with 6 hot spare disks is necessary -- at least not
when they're connected to the same server. Depending on the quality of your
disks 1 to 3 should suffice. With eg. 1 hot spare in the server plus some
cold spares in your office you should be able to survive a broken harddisk.
You should also "smartctl -t long" your disks frequently (ie once per week)
and do more or less permanent resync of your raid to be able to detect
disk errors early. (The worst case scenario is to never check your disks --
then a disk is broken and replaced by a hot/cold spare -- and raid resync
fails other disks on your array, just because the bad blocks are already
there...)

Hope this helps

-- Adi

-------------------------------------------------------------------------------------------------------------------

Hi Adi,

Thanks for the advice!

The RAID controller I'm planning to use is the MegaRAID SAS 9260-4i. The storage server will be built by Broadberry, so it will be using Supermicro kit.

As for the O/S on the server, I was thinking of using Windows Storage Server actually, however maybe this is a bad idea? You're correct about the live migration, however I may implement some sort of clustering iSCSI filesystem, however the main issue at the minute is the RAID array.

I've heard the same things about bonding 2 vs 4 NICs as well.

Currently, I'm leaning towards the RAID10 array with 14 disks with 2 hot spares

Thanks

Jonathan

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