Re: [Xen-users] iSCSI target - run in Dom0 or DomU?

[Matthew Wild <M.Wild@xxxxxxxx>]

On Friday 25 August 2006 13:50, Thomas Harold wrote:
> Javier Guerra wrote:
> > On Thursday 24 August 2006 7:10 am, Thomas Harold wrote:
> >> My plan for the disks is to lay software RAID over the disks (RAID1 for
> >> the first pair, RAID10 for the second set of 6 disks).  Then lay LVM on
> >> top of mdadm's software RAID before handing it off to iscsitarget to be
> >> divided up for use by the iSCSI initiators.
> >
> > do you plan to export the LVs over iSCSI?   i would advise to export the
> > PVs (/dev/mdX), and do CVLM on dom0 of the iSCSI initiators.  that way,
> > you could add more storage boxes (with more PVs) to the same VG
>
> Not sure yet.  The goal is to have a Xen setup where we can move DomUs
> between multiple head boxes on-the-fly.  Having a SAN should make this
> easier to do (if I've read correctly).
>
> And phase2 of the test project would be to have two, identically
> configured (roughly), SAN units that are either mirrored or
> fault-tolerant so that the Xen DomUs can keep running even if one of the
> two SAN units is down.  That also includes having 2 physical switches,
> multiple NICs bonded together (probably 2 bonded pairs, one for each
> switch) and multiple cables going to the switches (both for
> fault-tolerance and expanded bandwidth).
>
What I've been building is pretty much the same as this. We have 2 storage 
servers with 5TB usable storage each, replicating through drbd. These then 
run iscsitarget to provide lvm based iSCSI disks to a set of Xen servers 
using open-iscsi. The vitual machines are then set up using these physical 
disks. Because the iscsi devices can have the same /dev/disk/by-id 
or /dev/disk/by-path labels on each Xen dom0, you can create generic config 
files that will work across all the servers. Also, even though drbd is a 
primary/secondary replication agent at the moment, everything is quite happy 
for multiple Xen dom0s to connect to the disks, allowing for very quick live 
migration.

I haven't gone quite so far with multiple switches etc., but we are using 
VLANs to separate the dom0 traffic (eth0), domUs (eth1), and iSCSI (eth2).
All on Gb networking. We are also thinking of putting 10Gb links between the 
storage servers to keep drbd happy.

Matthew
-- 
Matthew Wild                       Tel.: +44 (0)1235 445173
M.Wild@xxxxxxxx                    URL http://www.ukssdc.ac.uk/
UK Solar System Data Centre and
World Data Centre - Solar-Terrestrial Physics, Chilton
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX

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