Re: [Xen-users] LVM over Xen + Network

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

On Mon, Oct 26, 2009 at 10:50 PM, rajan chandi <chandi.rajan@xxxxxxxxx> wrote:
> Thanks Javier for setup ideas.
>
> We are using ServerLoft Dedicated hosting.
> So, don't have much control over what can be done from a hardware
> perspective.
> Their servers are good and cheap.
>
> Only problem is that they don't support anything above 500 GBx2 with RAID 1.
>
> We are trying to figure a work-around to use the storage across the servers
> more efficiently.
>
> Is there a possibility to use LVM2 with some kind of NFS/GFS?

If by "efficiently" you mean "I need one server to have more storage
than what is physically available to it", then yes, it might be
possible. I'd generally say it's not worthed though. Way too much
effort.

For example :
- you have two servers with 500G disk each
- both is setup using partitions, one 50G (system) and one 450G (for
LVM PV). These are approximate values.
- you share second partition of server 2 using iscsi
- import iscsi share from server 2 on server 1
- setup LVM on server 1 using its own 2nd partition and server 2's
iscsi share. You'll get 900G VG.

Gotcha in this setup: if server 2 is dead, you might lose your data.
Workaround: you need 1 other server : say server 3. The setup now becomes:

- server 2 and server 3 share its partition using iscsi
- server 1 import iscsi share from 2 and 3, and setup it as mirror
using Linux md
- setup LVM on server 1 using its own 2nd partition and a mirror of
server 2 and 3's iscsi share

In this setup server 2 and 3 mirrors each other's data, so you can
have a single disk or stripe (RAID0).
Gotcha in this setup: you need to fine-tune iscsi so that in doesn't
retry forever when server 2 or 3 is dead.

See why I say it's too much effort?
It'd be MUCH easier to simply buy a 2U server with 14 3.5" drives,
have them host it (so it's colo instead of dedicated server), and use
it as iscsi/nfs server.

-- 
Fajar

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