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Re: [Xen-users] Alternatives to a dual-primary DRBD setup


Am 05/21/2011 02:16 AM, schrieb James Harper:
I would consider splitting up the storage and VM functions onto separate
servers. So 2 servers running DRBD and exporting LUN's via iSCSI (or AoE
or FCoE or whatever works for you) and then 2 (or more) servers running
VMs. This obviously needs more hardware though.

Unfortunately this is not possible at the moment due to limited budget. Besides this I expect other performance issues when introducing another layer like iSCSI or AoE to the game.

What I could do is to take for instance two harddisks into an own RAID1 being DRBD-replicated parallelly to the data but I guess this would make no difference to my current situation in the end.

I also thought about leaving the DRBD idea behind and to setup two independent servers, one holding the system backups and one being the productive machine if my systems couldn't cope with the DRBD thing. :-/

Another idea is to put the virtual systems onto the harddrive that the Xenserver host resides on (and not replicating them on-the-fly) and just leaving data on the DRBD-synced RAID5s.

The last both ideas would make XenMotion impossible which was the reason why I decided to run the Citrix solution. In that case I could possibly also run some newer (= better?) Xen version, i.e. under Debian Squeeze. :-/

Or some other idea that hasn't yet been considered...

Having said that, can you elaborate on the "sync issues" you are having
with DRBD? Anything that breaks under high load is still IMHO a bug and
can probably also break under low load, just less often, Are you running
the latest version?

No, it isn't the latest DRBD version (= Also my Citrix Xenserver isn't latest. It is still 5.6 without any FP or SP.

When I set up the virtualization system I saw everything running fine but the host machines weren't filled with virtual guests yet, unfortunately. It must be the (raised) amount of machines having reached an I/O performance consumption level that somewhen started concurring with the DRBD sync.

At least no system or data got harmed yet ... *knock knock* ... but it's not redundant at the moment. :-(

Currently when running a benchmark from one dom0 to the other (with "netio") I get throughput rates of > 200 MByte/s. And this is the speed that I used to have with DRBD, too. But as soon as I start syncing from the "younger" primary to the other DRBD machine my virtual guests' logs show timeout error messages.

In my investigations I read that a 10 GbE NIC can cause high CPU loads when not being configured properly. Is there possibly a way to reserve more of the CPU time and/or RAM for the Xen host/ dom0? I have plenty of CPU cores in the hosts and RAM is also far from being exceeded, still.


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