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