From: Johan De Meersman
Date: October 17 2012 11:30am
Subject: Re: Odd Behavior During Replication Start-Up
List-Archive: http://lists.mysql.com/mysql/228436
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> ----- Original Message -----
> From: "Reindl Harald" <h.reindl@stripped>
> 
> Am 17.10.2012 12:26, schrieb Johan De Meersman:
> > 
> > ----- Original Message -----
> >> From: "Reindl Harald" <h.reindl@stripped>
> >>
> >> i do not trust any FS snapshot in this context
> 
> > Why? I am completely unaware of any functional difference between an rsync and a snapshot, everything else being equal.
> 
> because you have to be pretty sure that you snapshot is consistent
> rsync the snapshot may result in the problem of the OP if there
> was not all written back to disk before the snapshot was made
> 
> the point of rsync in the way i make it is that mysqld is DOWN
> and it is only down for a very small timeframe because
> two rsync-runs, the first while mysqld is up and the
> second one after stop mysqld has only to copy diff

I agree with the double rsync - I use the same technique - but again, if your daemon is down (thus, everything else being equal) a snapshot is just as consistent as an rsync, no?

The main benefit of a snapshot, as far as I see, is that you don't have to do the I/O intensive first rsync - at the cost of copy-on-write operations after the fact, of course. Copy-on-write is blocklevel, though, so also has fairly little impact on performance save for extra metadata updates.





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