Re: [Xen-users] What's recommended method for serving data to/among DomU's?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I'm looking for comments/opinions on the pros & cons of various ways
> of serving data to DomU's ...
>
> Given a number of DomU VM's on a given box, data sotrage can take several
> forms:
>
>  (1) Data served via NFS from Dom0 to DomU
>  (2) Data served from a DomU-dedicated NAS, e.g., via NFS, OpenFiler, etc
>  (3) Data stored locally in each DomU
>
> The options above vary, at least, in security, performance, and backup
> strategy.

You could also consider network-based block devices, e.g. NBD or iSCSI to 
provide guest storage.  With these, you can use some kind of network storage 
server which may also be able to do block-based snapshots, backups, etc.  
They can also be used to facilitate live migration of VMs by making the VM 
storage accessible from multiple locations on your network.

Scripts are provided with Xen for setting up ENBD connections automatically.  
You can simply alter a domain's config file to give details of the ENBD 
connection, then dom0 will connect to the ENBD server automatically when the 
domain is started.  If the domain is migrated, the dom0 on the destination 
host will automatically connect to the ENBD server.  Through this technique, 
the use of networked storage is completely transparent to the guest, which 
just sees a normal Xen virtual disk.

My Ubuntu system includes scripts called block-enbd and block-nbd, presumably 
for different variants of the NBD server.

Something similar should be possible with iSCSI in order to make that 
transparent to the guest.  I've seen some patches posted on the mailing list 
to add the ability to do this automatically; they're not merged upstream, 
though.  An alternative would be to get guests to boot explicitly from an 
iSCSI root device; this isn't transparent to them but does still allow some 
of the same benefits.

Note that for any network based storage, you'll need to secure the storage 
server from abuse (e.g. domU's accessing each others storage, snooping 
network traffic, spoofing, etc).

Cheers,
Mark

-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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