[DRBD-user] protocol B in dual-primary mode

Marcus Sorensen shadowsor at gmail.com
Wed Dec 14 05:56:40 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.

Actually, the target we're playing with does handle reservations.
Thanks for confirming my suspicions, that this seems technically
feasible, but a bit hairy. Certainly would require a better
interconnect than ethernet and a simple crossover cable. I don't think
we'll end up going this route, but it sounds like it's at least worth
putting into lab and playing with it a bit.

I actually wouldn't mind doing failover, I'm just not aware of any way
to do it with fibrechannel short of some hardware that can share FC
cards between servers. We could perhaps spoof the wwpn of the target
and bring it up on the secondary in a failover, but that wouldn't
account for outstanding credits on the other device, and I certainly
don't think it would be as forgiving as TCP.

On Tue, Dec 13, 2011 at 12:00 PM, John Lauro
<john.lauro at covenanteyes.com> wrote:
> None of the open source targets will handle reservations or block locking.
> However, that point is moot when you have a single client multi-pathing to
> drbd pair, but reservations are very critical for SAN based filesystems...
> Assuming only a single client to two DRBD nodes and doing failover, it is
> very risky as the slightest network hiccup can cause a split brain as the
> default timeout retries are extremely low and despite having protocol C,
> one node might thing the other is down when it is not really.  However, if
> (and only if) you truly implement STONITH so split brain is impossible, as
> far as I can tell you could do multi-pathing despite all of the comments
> not to do it.
> So two requirements:
>        1. No multi-node to same resource.  (No SAN type filesystem).
>        2. STONITH must be implemented.
> If you meet those two requirements, then it should technically be
> possible, but comes down to a why bother with active/active multipath DRBD
> at all, and why not just fail over the service on top of DRBD.
>> -----Original Message-----
>> From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-
>> bounces at lists.linbit.com] On Behalf Of Felix Frank
>> Sent: Tuesday, December 13, 2011 4:44 AM
>> To: Marcus Sorensen
>> Cc: drbd-user at lists.linbit.com
>> Subject: Re: [DRBD-user] protocol B in dual-primary mode
>> Hi,
>> On 12/13/2011 05:35 AM, Marcus Sorensen wrote:
>> > What if you're just
>> > exporting drbd block, active-active devices via say, iscsi or SAS
>> > target? Couldn't the initiator just treat them as the same disk,
>> > multipathed?
>> there was a lengthy discussion last week or the one prior on why you
>> cannot do that. Long story short, two state of the art iSCSI targets
>> cannot operate as one multipath target.
>> I can't seem to find it quite on the spot, but a quick trawl through the
>> archives should yield some info.
>> Cheers,
>> Felix
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