North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: Scalable Mail solution with NAS

  • From: Adrian Chadd
  • Date: Wed Jan 31 15:50:51 2001

On Wed, Jan 31, 2001, Matthew Zito wrote:

> No, no, don't do that.  Given the scale of something like this, I'd expect 
> you'd be running on something like Oracle that supports the concept of "hot 
> backups".  The table spaces are put into a quiesced state, and all writes are 
> done to memory and to recovery logs.  Once the backup is finished, you take 
> it out of hot backup and it then writes all the pending transactions to the 
> database files. That way, the database files are stable, and you also back up 
> the recovery logs to something with real-time access (like another nfs 
> server).  In the event you have a catastrophic database failuser, you recover 
> from tape (or if you have the space, you have a copy of the dbf files 
> elsewhere), and run all the transaction logs - it takes about 5 minutes per 
> hour of transactions.  Then your database is brought up to the point where it 
> was when it died.  The worst case scenario is that there's a few transactions 
> that don't get logged, which means that a few emails get dropped.  If you had 
> a stock smtp server that died, you could be looking at the same situation.

.. and then you have to make sure that you periodically garbage collect
your local store, lest you end up with a whole bunch of files which are
unreferenced and just take up space. :)

> As far as backing up the actual mailboxes, there's no way to get around the 
> fact that it'll take long enough to finish that stuff will be inaccurate by 
> the time its finished.  If you ever have to restore the mailboxes from tape 
> without restoring the database, it'd be wise to have an application that 
> builds a list of the messages that are on disk the database doesn't know 
> about.  

At least two commercial filesystems support "snapshots" - AdvFS and
WALF (NetApp). I don't remember if XFS supports snapshots.
Oh, FreeBSD's FFS has got snapshot capabilities but its not yet useful
in a "real world" scenario.


Adrian
-- 
Adrian Chadd			"Sex Change: a simple job of outside 
<[email protected]>	  to inside plumbing."
				    - Some random movie