Yeah but that's databases! Whole different game. ;)

Jason
Sent from my iPhone 5S

> On Mar 16, 2014, at 8:28 PM, roemer <uwe.ro...@gmail.com> wrote:
> 
>> On Monday, 17 March 2014 06:40:02 UTC+11, cap wrote:
>> An advantage of snapshots is with active filesystems such as those used by a 
>> database.  For a consist at database backup you of course need to stop the 
>> program then backup then restart ( or use some database tool if available) . 
>>  The time to create a snapshot is essentially zero so the above start - stop 
>> is actually practical.  Then you use your backup software of choice on the 
>> snapshot not the active file system.
> This is only fine if your database is read-only or you have control on the 
> update workload.
> Most database systems use a combination of no-force+steal buffering and WAL 
> logging (e.g. MySQL InnoDB or PostgreSQl and basically all commercial RDBMS).
> Taking a file-system level snapshot underneath does not guarantee that you 
> get a consistent snapshot of the database log and data pages.
> Together with high update rates, this can be dangerous. Better use the 
> database system's snapshot facility too before you take the ZFS snapshot. 
> Granted, open source systems are a bit weak in that regard...
>   
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