On 11/4/2013 1:27 PM, Phil Stracchino wrote:
> On 11/04/13 13:00, Josh Fisher wrote:
>> I would add that it is critical (IMO) to place the DB storage on
>> different physical drives than those holding the Bacula spool area. At
>> the end of a job Bacula SD must read the spooled attributes and update
>> the catalog. If spooled attributes and catalog are on the same spindles,
>> then the disk thrashing negates the advantage of attribute spooling. I
>> might also add that placing the catalog on SSD resulted in a hefty
>> performance gain.
> Seconded.  Wherever possible, you always want your DB either on separate
> spindles or on solid-state media where seek latency is not an issue.
>
>> As for clustering using DRBD, the catalog and spool area should still be
>> on different spindles.
> Honestly, based upon experience as a DBA at a hosting company that hosts
> MANY customers using MySQL, my first advice on using MySQL on top of
> DRBD would be "Just don't."  I could cite lists of customers who have
> had complete unrecoverable DB losses as a result of problems or
> interactions involving DRBD, and had to rebuild from DB backups.  If
> you're going to cluster MySQL, use a shared-nothing configuration if you
> possibly can.

Interesting. I am curious as to what DRBD replication mode was used. In 
mode C (synchronous replication) a write operation does not complete 
until it has been written to both nodes, so is essentially network 
RAID-1 and guaranteed not to lose data in the event of a forced 
fail-over. It is of course slower, so some may be tempted to use mode A 
(asynchronous replication) which can and will lose data in the event of 
a fail-over. Mode A is faster and reasonable for some uses, but only 
mode C should ever be used for database storage. I have been using MySQL 
on DRBD in mode C for quite some time and have seen drive failures, NIC 
failures, and node failures without any data loss or db problems I could 
attribute to DRBD.


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