Anyone whose ever had to rebuild a server just fromtapes might agree

[John Macdonald]

On Thu, Jan 08, 2004 at 06:14:59PM -0500, CLIFFORD ILKAY wrote:
> At 02:38 06/01/2004 -0500, John Macdonald wrote:
> >On Mon, Jan 05, 2004 at 10:52:04PM -0500, cbbrowne-HInyCGIudOg at public.gmane.org wrote:
> >> The only relatively "safe" way to get a quasi-atomic backup is to use
> >> LVM, so that you can atomically "split off" a temporary copy of the
> >> filessystem.  That makes the backup "atomic," which can allow satisfying
> >> databases' needs for consistency.  You may need to recover the database,
> >> but that usually fits into its design.
> >
> >With IBM's DB2 UDB database, there is an improvement
> >to be made to this process.  It has a command to
> >suspend write IO (which also updates the log before
> >stopping writes).  Then you can split off a copy,
> >and resume writes.  The copy can then be restarted (no
> >recovery required).  Since it is only writes that are
> >suspended, read transactions are not blocked at all,
> >and write transactions can be carried out up to the
> >point of committing (which then has to wait for the
> >write resume).  Depending upon the mechanism used to
> >split off the copy, this can be a very fast operation
> >- using EMC Symmetrix storage array, I split off a
> >copy of a 64 MB database with writes suspended for
> >only a few seconds.
> 
> I take it this is/was a VC backed dot com:) That sounds like an awful lot 
> of overkill just for a database that would fit on a Zip drive or a USB pen 
> with room to spare. I presume you did not mean 64GB. It would not take much 
> longer to shut the DBMS down, copy the files, and start it back up with 
> PostgreSQL but then you would not have to do that anyway with pg_dump since 
> pg_dump will make consistent backups of live data.

Blush, yes, that was 64 GB, not MB.  (The Symmetrix
described above had 4 TB of disk space on it, but the
new one that has since replaced it has about triple
that - 96 drives of 147 GB each under the hood.)
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