RE: [Xen-users] Xen SAN Questions

["Tait Clarridge" <Tait.Clarridge@xxxxxxxxxxxx>]

Well I ran the numbers and made the changes and they helped a little bit, but I 
am thinking that the non Primary/Primary setup is what really helped.

The setup I think I am going to go with is 2 Hardware RAID5 arrays connected 
using DRBD and formatted as XFS.

Once I actually get the arrays setup and connected I will try a DD (I am 
testing on two servers that are older and much slower than the ones we are 
going to put into production as our xen hosts) and let you know if the final 
average speed.

Thanks to everyone for their help!


Best,
Tait Clarridge


-----Original Message-----
From: Fajar A. Nugraha [mailto:fajar@xxxxxxxxx] 
Sent: Wednesday, January 28, 2009 10:01 AM
To: Tait Clarridge
Cc: xen-users list
Subject: Re: [Xen-users] Xen SAN Questions

On Wed, Jan 28, 2009 at 9:09 PM, Tait Clarridge
<Tait.Clarridge@xxxxxxxxxxxx> wrote:
> Well I figured out one thing, that my numbers were totally off for EXT3 and 
> XFS without DRBD haha.
>
> I will do some more testing, I can't believe I ruled out "dd" as a viable 
> benchmark.
>
> *smacks forehead*
>
> Thanks for the help, I am testing with those DRBD config options now.

I'd be interested to hear about your results.

To tell the truth, I was tempted to try a similar setup. I decided
against it though, because :
- using local disks provide higher I/O throughput. Using
network-attach disks, however, is mostly limited by the network
interconnect speed. For example, 1 Gbps network link could only give
max (theoretical) throughput of 125 MBps while local disks can easily
give 235 MBps (tested with dd)
- active-active DRBD setup can produce split-brain

So in the end I settled for scheduled zfs-based backup. That is :
- when using opensolaris dom0, I can use zvol-backed storage and do
backups from dom0
- when using Linux dom0, I use zfs-fuse on domU and perform backups there.

Again, I'd be interested to hear about your results. If you can get
something like 200 MBps then I'd probably try to implement a similar
setup.

Hint : You probably want to stay away from GFS as domU's backend
storage. Just use LVM-backed storage (with cLVM, of course) for MUCH
faster performance. To measure its performance, a simple way is using
dd on the block device.

Regards,

Fajar



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