[DRBD-user] Cluster filesystem question

Digimer linux at alteeve.com
Thu Dec 1 20:25:45 CET 2011

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

On 12/01/2011 02:22 PM, Jake Smith wrote:
> ----- Original Message -----
>> From: "Digimer" <linux at alteeve.com>
>> To: drbd-user at lists.linbit.com
>> Sent: Thursday, December 1, 2011 2:18:42 PM
>> Subject: Re: [DRBD-user] Cluster filesystem question
>> On 12/01/2011 02:13 PM, Lars Ellenberg wrote:
>>> On Thu, Dec 01, 2011 at 01:58:15PM -0500, Kushnir, Michael
>>> (NIH/NLM/LHC) [C] wrote:
>>>> Hi Lars,
>>>> I'm a bit confused by this discussion. Can you please clarify the
>>>> difference?
>>>> What I think you are saying is:
>>>> OK:
>>>> Dual-primary DRBD -> cluster aware something (OCFS, GFS, clvmd,
>>>> etc...) -> exported via iSCSI on both nodes -> multipathed on the
>>>> client
>>> No.
>>> OK:
>>> Dual-primary DRBD (done right) -> cluster aware something (OCFS,
>>> GFS, clvmd, etc...)
>>> NOT OK:
>>> -> exported via iSCSI on both nodes -> multipathed on the client
>>> NOT OK:
>>> anything non-cluster-aware using it "concurrently" on both nodes.
>> What I've done in the past, and perhaps it isn't the wisest (Lars,
>> Florian?), is to create a Dual-primary DRBD (with fencing!), then
>> export
>> it as-is to my nodes using a floating/virtual IP address managed by a
>> simple cluster.
>> Then on the clients (all of whom are in the same cluster), I mount
>> the
>> iSCSI target and set it up as a clustered LVM PV/VG/LVs. If you need
>> a
>> normal FS, then format one or more of the LVs using a cluster-aware
>> FS.
>> When the primary node (the one with the floating IP) fails, all the
>> cluster has to do is move the IP down to the backup node and it's
>> ready
>> to go. I suppose you could just as easily do Primary/Secondary and
>> include the promotion of the backup to primary as part of the
>> failover,
>> too. In my case, knowing I had fencing in place already, I went for
>> the
>> "simpler" cluster config of managing an IP only.
> I could be totally wrong but from what I read above you're not multipathing on your clients; just speeding up failover times; so (IMHO) you fit the "OK".  But I'm sure one of the experts will weigh in.
> :-)
> Jake

This is true, I avoided multipath. I've heard too many difficulties with
it's use, so I preferred simple/reliable over instant, particularly
given iscsi's inherent robustness.

In my case, the iSCSI-backed LVM LVs were used to host VMs. In one
failure test, the fence failed and it was close to 30 seconds before I
corrected the problem and recovery completed. Even in this long case, my
VMs didn't fail (though they did block on disk i/o, of course).

Again though, my experience only and I'm claiming no expertise. :)

E-Mail:              digimer at alteeve.com
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