[DRBD-user] DRBD dual primary mode implications

Paul Mackinney paul.mackinney at ondiagnostics.com
Tue Mar 3 18:26:39 CET 2015

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Apologies in advance if this is too off-topic for this forum, feel free to
reply directly & point to other resources.

I'm having good success with DRBD in the following configuration:

Two identical hosts, dual-bonded ethernet for DRBD with a dedicated VLAN on
my smart swtich.

I'm running DRBD on top of LVM, each device is the backing storage for a
KVM virtual guest. The top-down diagram is:

[/dev/sda1] Guest root system
[ /dev/sda ]
[ /dev/drbdN ] <--- primary/secondary mode
[ /dev/mapper/vg-lvN ]
[ lvm physical volume ]

This works perfectly, but guest migration requires a shutdown:
1. Shut down guest on host 0
2. Demote DRBD primary to secondary on host 0
3. Promote DRBD secondary to primary on host 1
4. Start guest on host 1

Apparently running GFS with DRBD's dual-primary mode would allow KVM
migration from one host to another without a shutdown, but all the
tutorials jump straight into cluster configuration.

Is converting my hosts into a cluster really the next step? Of course the
point of KVM migration is to get to automatic failover.

Paul Mackinney
Systems & Quality Manager
O.N. Diagnostics, LLC
2150 Shattuck Ave. Suite 610, Berkeley, CA 94704
510-204-0688 (phone) | 510-356-4349 (fax)
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