Largest file system being synced

[jw schultz]

On Thu, Jun 27, 2002 at 02:21:08PM -0400, Granzow, Doug (NCI) wrote:
> We're planning to move to Veritas Volume Replicator.  It has the advantage
> of working at the filesystem level, so whenever a write is done on the
> primary site, the same write is automatically done on the mirror site.  For
> what I am doing here, it should (hopefully!) work a lot better than rsync
> because it runs continuously, and it doesn't have the startup overhead of
> building a file list, which is the biggest problem with rsync when you are
> dealing with large groups of files.

Unless this is a new product I've used it.  It works fairly
well and unlike most Veritas products the error messages
actually mean something.  It has been about two years so
this could be a new product but the one i dealt with was
really meant to be used as part of a N second fail-over
solution with heartbeats et al.  I give my comments here
to further general knowledge and so you can hear from someone
other than a Veritas spokes-being.

It doesn't work at the filesystem level.  It works at the
block device level.  Every time a block is modified it is
queued for transmission to the mirror(s).  If the same block
is queued twice there is no coalescence, it will be sent
twice.  We did it over a VPN and Oracle kept sending the
same block over and over every five seconds due to an
acknowledged Oracle bug.

There are three caveats to be aware of. You will get more
network traffic than you probably expected.  Only one
end of the connection can be used at a time.  And the
filesystem on the mirror(s) is in the same state it would be
if you pulled the plug so to go on-line requires the
filesystem to replay the journal.

It served the purpose, over a VPN needed more babysitting
than i liked, but it did work fairly well but i disagree
with the approach.

> 
> 
> 
> > -----Original Message-----
> > From: Breedlove, Robert [mailto:RBreedlove at caiso.com]
> > Sent: Thursday, June 27, 2002 11:46 AM
> > To: Granzow, Doug (NCI); 'rsync at lists.samba.org'
> > Subject: RE: Largest file system being synced
> > 
> > 
> > What are you moving to?
> > 
> > -----Original Message-----
> > From: Granzow, Doug (NCI) [mailto:granzowd at mail.nih.gov]
> > Sent: Thursday, June 27, 2002 8:31 AM
> > To: 'rsync at lists.samba.org'
> > Subject: RE: Largest file system being synced
> > 
> > 
> > 
> > I am currently syncing 1.3 terabytes of files using rsync.  
> > This is spread
> > across about 12 filesystems all on the same server.  
> > Unfortunately we are
> > planning to move away from rsync because it is taking too 
> > long to run and it
> > takes up too much memory (some of the rsync processes take up 
> > 1.5 GB of RAM
> > -- if we get two of those running at once, the server dies).  
> > We have been
> > very happy with rsync but it has recently reached a critical 
> > mass where it
> > can no longer handle the number of files we are trying to 
> > sync in a timely
> > manner.   But if you are looking for the largest rsync site, 
> > we might be a
> > contender. :)
> > 
> > FYI, we also use (and plan to continue to use) rsync for 
> > several smaller
> > mirroring operations.
> > 
> > 

-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt