[clug] iSCSI and shared filesystems

steve jenkin sjenkin at canb.auug.org.au
Fri Apr 23 20:59:43 MDT 2010

Brett Worth wrote on 23/04/10 10:28 PM:

brett - thanks very much. nice to hear real war stories.

> I've actually used this.  I was serving LUNs with ietd on Linux and connecting using the
> iSCSI initiator on Linux too.
> I've done some experimentation with shared filesystems for Xen migration.  I guess how you
> do it will depend on what you're trying to achieve with the migration.

Somehow in previous post and from the on-line "HowTo", I got the idea I
didn't have to use a shared filesystem within the DomU's. ie. ext3 would
cut it.

> Were you thinking of using the iSCSI for the root filesystem?

Sorry, now confused.
Root filesystem of Dom0 (host) or DomU (guest)?

My intention was to have local filesystems for DomO and 2 shared
filesystems for DB-data and DB-logs in the DomU, thinking LVM.

Not sure how to make & store the DomU images.

> If that's the case then I
> think you need to have the Xen dom0 machines acting as initiators to what ever is serving
> the iSCSI e.g. your NAS box.  So you'd end up with /dev/XX devices on them which the Xen
> config files would point to.
> I've currently got a pair of Xen machines that run a shared filesystem using OCFS2.  These
> are sharing LUNs with Fibre Channel but you could do exactly the same thing with iSCSI.
> The OCFS2 is a bit sensitive to storage problems and tends to self-fence (by panicking)
> for the slightest reason so you'd need to test it.


> If you can use a shared filesystem, even NFS, for the root images it makes maintenance
> much simpler..   Maybe get the NAS box to do NFS for the root then share some raw storage
> with iSCSI for the database.  You could run into performance problems with the iSCSI.
> There's a few recommendations for how to setup the network and tcp offload is at the top
> of the list from memory.
> Just this week I was also playing with GFS on RedHat but have only used it on a single
> node so far.  It's all I could find that could create a 32TB filesystem that actually came
> with RedHat.  BTW even though the doco says that ext4 support VERY large filesystems it
> seems that the tools (mkfs, fsck etc...) are still limited to 16TB.  Maybe  RHEL6.
> Anyway GFS might be a good shared filesystem for Xen machines with iSCSI if you can get
> the cman bits to work on a network.
> Brett

Steve Jenkin, Info Tech, Systems and Design Specialist.
0412 786 915 (+61 412 786 915)
PO Box 48, Kippax ACT 2615, AUSTRALIA

sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin

More information about the linux mailing list