[Users] Re: vzmigrate standby mode

[Tim Small]

On 18/05/11 12:30, Tim Small wrote:
>
> We use a hacked version of mylvmbackup to backup an entire container. 
> Each container lives on its own logical volume, and the process calls
> into the logical volume to ask the database (mysql in this case) to make
> its data-on-disk consistent.  At this point, and LVM snapshot is taken,
> then mysql is told it can carry on writing to disk.  The LVM snapshot is
> then fscked and mounted on a different mountpoint, once mounted, the
> contents are rsynced to the standby machine, and the lvm snapshot is
> removed.
>   

I should add that this is done at a relatively quiet time on the server
(if it's a server with lots of writes), as it has the side effect of
turning a single write on the containers storage into two writes and a
read (plus associated disk seeks) whilst the LVM snapshot exists.

Whilst the lvm snapshot is being created (< 1 second), writes to the
database block (reads continue as normal, however), then continue once
mysql gets the UNLOCK TABLES command.  I don't know if there is
equivalent functionality available in other databases such as PostgreSQL
etc.

Cheers,

Tim.

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