On 2014-02-28T13:16:33, Digimer <li...@alteeve.ca> wrote:
> Assuming a SAN in each location (otherwise you have a single point of
> failure), then isn't it still possible to end up with a split-brain if/when
> the WAN link fails?
As I suggested a 3rd tie-breaker site (which, in the case of SBD, can be
any old iSCSI LU somewhere), no, this can't happen. One site would fence
the other.
(The same is true, if a bit more elegantly, for booth.)
> Something (drbd?) is going to be keeping the data in sync between the
> locations. If both assume the other is dead, sure each location's SAN will
> block the other node, but then each location will proceed independently and
> their data will diverge, right?
For a two site setup, perhaps. A manual fail-over would need to make
sure that the other site is really stopped.
Assuming two sites, the currently active site would not be able to
commit new transactions as long as the WAN link is down and the other
site has not been declared dead (through automatic or manual fence
confirmation).
Also, any replication mechanism includes a means to pick a winner and
sync over such divergent changes, should they occur. Which they
shouldn't.
(Asynchronous replication on the other hand always has a RPO > 0, and
can always risk losing "a few" transactions. That is the nature of
disaster recovery. Hopefully, disasters are rare.)
Regards,
Lars
--
Architect Storage/HA
SUSE LINUX Products GmbH, GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB
21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde
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