Re: [Xen-users] Network Storage

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Tue, Jan 20, 2009 at 11:53 PM, lists@xxxxxxxxxxxx <lists@xxxxxxxxxxxx> wrote:
> Another area of problems is that of using network storage.
>
> In my case, I'm using legacy 1GB and 2GB fibre channel storage units 
> connected into fc filers that hand off NFS/CIFS. It's a nice, simple setup 
> but in trying various combinations, things are still very slow and sluggish.
>
> I've tried various things such as having an NFS or direct FC share onto each 
> VM server, then installing the guest onto the network storage. Works fine but 
> when you start adding servers, things get a bit difficult.

The way I see it, when it comes to storage allocation, it's probably
best (in terms of balance between performance and managability) to
treat xen domUs like any other physical server. You allocate a
different LUNs for each domU. Other than giving higher I/O
performance, this method has the added benefit that it allows easy
converting between domU <-> real servers.

> The servers run just fine, nice and fast but, the gotcha so far, seems to be 
> when copying files across that storage for any of the servers. So for 
> example, when copying say large backup files, GB sized, that slows down 
> everything way too much.
>

Yeah, I know.
For a long time we used to centralize every storage on 1 & 2 Gbps FC
SAN. This works fine for the most part, until we put I/O-hungry
applications on it. Oracle database was competing for I/O with web
servers, making performance of both suffer greatly. In the end we find
that local storage actually provides MUCH higher I/O throughput, since
it has "dedicated" disks with plenty of I/O bandwitdh :p

So bottom line, my suggestions are :
- treat domU's storage like real server's storage
- usual I/O optimizations apply : more disks for more throughput, have
lots of available BW, dedicated storage when possible, etc.

As a side note, if you're already familiar with FC filers, you might
want to try SUN's new Unified Storage or even a simple
OpenSolaris-based NAS. You can then use iscsi-exported zfs-volumes
which gives you features like :
- snapshot and clones (can save space significantly, plus making
things like backup a lot easier)
- compression (also a space-saver, and might even increase I/O
throughput in certain conditions)
- chekcsums and raidz to ensure data integrity

Regards,

Fajar

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