On 06.10.2010 11:39, Markus Wanner wrote:
On 10/06/2010 10:17 AM, Heikki Linnakangas wrote:
On 06.10.2010 11:09, Fujii Masao wrote:
Hmm.. but we can increase availability without any data loss by using
synchronous
replication. Many people have already been using synchronous
replication softwares
such as DRBD for that purpose.
Sure, but it's not the synchronous aspect that increases availability.
It's the replication aspect, and we already have that.
..the *asynchronous* replication aspect, yes.
The drdb.conf man page [1] describes parameters of DRDB. It's worth
noting that even in "Protocol C" (synchronous mode), they sport a
timeout of only 6 seconds (by default).
Wow, that is really short. Are you sure? I have no first hand experience
with DRBD, and reading that man page, I get the impression that the
timeout us just for deciding that the TCP connection is dead. There is
also the ko-count parameter, which defaults to zero. I would guess that
ko-count=0 is "wait forever", while ko-count=1 is what you described,
but I'm not sure.
It's not hard to imagine the master failing in a way that first causes
the connection to standby to drop, and the disk failing 6 seconds later.
A fire that destroys the network cable first and then spreads to the
disk array for example.
[1]: drdb.conf man page:
http://www.drbd.org/users-guide/re-drbdconf.html
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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