RE: [Xen-users] Best way to store domU's. NFS? NBD?

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Wiebe Cazemier
> Sent: Wednesday, March 24, 2010 1:15 PM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Best way to store domU's. NFS? NBD?
> 
> Hi,
> 
> I'm trying to find out what the way is to store the domU disk images,
keeping
> live migration and failover in mind. One source [1] says NFS is the
most
> common. Another source [2] says that NFS is flaky. Then iSCSI is
mentioned as
> very robust, but the xen wiki makes not a single mention of that.
Also, (E)NBD
> is mentioned.

Decide whether you want files or block devices as the backing store of
your domU's.  There are pros and cons to each.  In my installations I
work solely with block devices, so I won't discuss NFS further.

DRBD does a great job of providing shared, reliable block devices for
two-node Linux clusters.  It requires a good network connection but no
specialized hardware.

iSCSI is nearly ubiquitous among commercial SAN products these days.
Its main advantage is interoperability--there are many SAN vendors, many
client implementations (Linux and otherwise), and works over any network
that supports TCP/IP.  You can also use a Fibre Channel SAN or even
FCoE, AoE, or any of the lesser-known protocols.  It may make more sense
to choose a good storage vendor, using their recommended and supported
protocol, than the other way around.

GNBD is available for those who don't wish to invest in a commercial SAN
(as is DRBD), but I don't believe GNDB is receiving further development.

No matter what you choose for shared block storage, you need some kind
of logical volume management so you can easily carve up your large
physical RAID arrays into manageable pieces to store individual disk
images or filesystems.  Many SAN products include management tools that
make this easy.  Some offer handy features such as thin provisioning or
volume snapshots.  For Linux installations, Red Hat's Clustered LVM
(CLVM) can also provide volume management independent of whatever
network storage you choose, and is simple to deploy on RHEL or CentOS
clusters.

What is "best" may well depend on your exact requirements.  Do you need
simple failover (2 machines) or might you need to grow to 3 or more
hosts?  How much storage overall do you need today, and are you prepared
to grow this on demand?  Are you running a homogenous Linux environment
or do you need to mix in Windows or other systems?  What will you use to
backup data?  (And so forth.)

-Jeff



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