[DRBD-user] drbd+mysql+innodb

Robinson, Eric eric.robinson at psmnv.com
Thu Jun 13 06:29:56 CEST 2013

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

I really appreciate everyone's input but everyone misunderstood the question I was really asking. It's my fault for mentioning rsync. I fully understand the difference between how rsync works and how drbd works. We use them both all the time. But the real question is more high level. We have been told that even if you stop the mysql service, you still cannot backup an innodb database by simply copying the files from one server to another. We have been told that the mysql service will not start properly on the new server even if you make a 100% exact copy of all the files from the old server. If that is true, I don't understand how using drbd can work with innodb tables, since it basically just makes a copy of the files to another server. Am I asking the question right?

Eric Robinson

From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Adam Goryachev
Sent: Wednesday, June 12, 2013 6:58 PM
To: drbd-user at lists.linbit.com
Subject: Re: [DRBD-user] drbd+mysql+innodb

On 13/06/13 10:37, Dan Barker wrote:
rsync will not be able to synchronize from a "failed" disk, drbd already has done so.
Dan in Atlanta
From: drbd-user-bounces at lists.linbit.com<mailto:drbd-user-bounces at lists.linbit.com> [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Robinson, Eric
Sent: Wednesday, June 12, 2013 6:20 PM
To: Dirk Bonenkamp - ProActive
Cc: drbd-user at lists.linbit.com<mailto:drbd-user at lists.linbit.com>
Subject: Re: [DRBD-user] drbd+mysql+innodb
Hi Dirk - Thanks for the feedback. I do need some clarification, though. DRBD replicates disk block changes to a standby volume. If the primary node suddenly fails, the cluster manager promotes the standby node to primary and starts the MySQL service. Logically, this seems exactly the same as simply rsyncing the data to the new server and starting the MySQL service. Why would it work with DRBD but not with rsync? Thanks for your patience while I explore this.
Note: we have over 500 separate MySQL database instances using MyISAM. I am totally not stoked about the idea of using 300% more disk space and gobs more memory.

I think the real issue with rsync is that it will start copying the file, but new writes may come in during the copy process, therefore the destination copy is not a point in time copy of the source. This is the same issue with using rsync for disk images of VM's that are running during the rsync. As explained, this is not an issue for DRBD replication, because at any instant in time, the replica (destination copy) is an exact copy of the source at some point in time, even if it is not the latest point in time.


Adam Goryachev
Website Managers

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