[Xen-users] Multi-server setup, storage question

[Henric <henric@xxxxxxxxxxx>]

Hi,

To make life easier, this e-mail is divided in three sections 
(background/specs, question, goal).
First some information that might be useful to the question further 
down.
I have two identical servers as per this config:
 - 8 cores each
 - 64 GB ram each
 - HW-RAID backed storage (~695 GB/SAS 15k RAID6)
 - Quad Gigabit NIC
 - Linux 18.1 (currently)
 - Xen 4.4.1 from openstack's gplhost repos (currently)
 - Debian Wheezy with Backports (currently)

I am looking to run all the XEN guests from the local hw-raid storage 
and use LVM for the guest disks.
I am using local storage as opposed to an iSCSI SAN since performance / 
latency is very important in this project.

Now for the question:

Is it a good idea to use a distributed file-system to make "one big 
slab" of LVM storage and then set up guests disks on that?
Or should I use DRBD to mirror the whole storage between the servers?

Ideally I would want to be able to use both machines to run guests at 
the same time, but I am quite happy to have one server on "hot standby" 
too.
But I am unsure about the performance impact a distributed file-system 
would have?
And which one to choose if that was the case?


The goal:
To have full hardware fail-over.

Let's say server 1 has a catastrophic failure, then I want to be able to 
retain all the data and start the guests on server 2.
DRBD would solve this, since it could mirror the whole "storage surface" 
between server A and server B.
But if I had a distributed filesystem, then ideally I could run guests 
on both server A and B at the same time.
And if server A or B died, I would still have all the data and be able 
to run the guests on the surviving server (since I will not 
over-provision storage over the ~695GB available).

--

Henric Blomgren

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