Re: [Xen-users] Can guests share an FC HBA?

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

On Mon, Jan 26, 2009 at 11:35 AM, lists@xxxxxxxxxxxx <lists@xxxxxxxxxxxx> wrote:
> Nick mentioned that the host can share it's drives/storage so this has made 
> me wonder about something.

I think we're talking about two different things here. I was talking
about how a guest can share hosts' HBA so each guest would think they
have their own "dedicated" HBA. This is needed for some situations,
for example tape backups.

Sharing a drive/storage (as in block device, not the fs) should simply
be mapping host's storage using the usual phy:/ vbd, and (optionally,
if multiple guests access the same storage) some kind of clustered fs.
Note that there are also methods like using tap:qcow to have multiple
guests share reads to the host's block device while writes are
redirected to a different file.

Sharing host fs is done using the old NFS/CIFS method.

>
> In my testing so far, each guest usually has NFS mounts to a central storage. 
> I don't know the NFS protocol well so am only guessing that such a connection 
> means chatter on the network.

Yes.

>
> So, if there are say 10 guests on a server, each connected to the shared 
> storage via NFS, this would end up being a ton more Ethernet chatter than it 
> would if I could simply connect the storage ONCE to the host, then give each 
> guess access to this.

I get your point, but AFAIK it would not reduce network traffic as NFS
makes very little use (if any) of cache, so that all traffic would end
up in the NFS server anyway, which is why on the other thread I
mentioned you should have a dedicated storage network.

You might have better luck with cachefs to reduce NFS network traffic.

Regards,

Fajar

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