The thing about a snapmirror *volume* is that the entire thing is
read-only.  Unlike a volume of qtree snapmirror's where the volume is
read-write but the qtrees are read-only.  This means no snapshots can be
taken of a snapmirror'd volume.  At least I'm pretty sure that's the way
it goes.  If not someone will speak up.

As for backup speed, it's pretty dependent.  Even though NBU does not
multi-plex NDMP (there's nothing specific to NDMP that prevents it from
doing so, simply Veritas' *inability* to make it so) a single volume can
easily flood gigabit, so a tape drive is child's play to drown.
That being said, a filer's primary function is to serve data.  Any other
function is secondary and is always interrupted by said process.
However the filer can not differentiate between NFS traffic of one type
or another, so if you do backup over NFS it will get the same priority
as all other file serving processes.  Usually this means little but on a
very busy filer it can make a difference.
Of course that also means users suffer from poorer performance because
backups are eating into their process time but that's a case-by-case
call.

~JK

-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu] On Behalf Of Tim Berger
Sent: Saturday, April 02, 2005 1:20 PM
To: Algo Seeker
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] snapmirrored volumes question

Right, with snapmirror, you don't have any significant lag to worry
about, and by listing entire volumes instead of qtrees, managing
snapshots for backing up over NFS is easy.  I do not believe you are
in any danger of backing up corrupt data if the snapmirror is
'transferring', but I would try to avoid that if possible. It's fine
to run backups in the 'quiescing' state.  I don't believe the method
used, be it NFS or NDMP has any bearing on this.

As far as which yeilds better performance, you just have to try that
for your environment.  Certainly, you'll want to stream your tape
drives by whatever means possible.  To perform a fair comparison,
don't go 3-way NDMP.  Go direct or through a SAN if you can. 
Traditionally, NDMP has yeilded better performance, but with recent
super high speed tape drives and netbackup w/NDMP continuing
*inability* to multiplex, you might be better of with NFS.

If you list entire volumes, all qtrees under it get backed up.  Use
separate policies for every volume so you know which snapshots to
manage in your <polname>.bpstart_notify and <polname>.bpend_notify
scripts.

Have you tried both methods?  You ought to be able to get a temporary
NDMP license from your sales rep.  What model filer are you using,
what types of drives are you using, and what data rates are you
seeing?  Just curious.

NDMP with netbackup is turning out to be disappointing.  No
checkpointing.  No drive sharing.  No multiplexing!

On Apr 2, 2005 6:42 AM, Algo Seeker <algorithm AT gmail DOT com> wrote:
> Well my problem is the mirrored volumes are always in a lag of 30
> minutes toan housr and ar in never idle state.  Now in that scenario,
> what would be the best way to backup.
> 
> I do have huge number of qtrees and I do not want to add those in my
> selection list and just want to add volumes.
> 
> Thanks
> On Apr 2, 2005 1:36 AM, Tim Berger <tim.berger AT gmail DOT com> wrote:
> > snapvaulted/snapmirrored volumes are treated no differently than any
> > other volume when using NDMP.  You specify qtrees in the include
list.
> >  Snapshots are made on-the-fly.
> >
> > However, I recommend creating an ndmp_start_path_notify script to
> > check for volumes that are still "Transferring" data and fail out to
> > re-queue the job if this is the case.  This will avoid backing up
> > yesterday's vault data.  Adjust your media server's retries per hour
> > accordingly.
> >
> > On Apr 1, 2005 9:01 PM, Algo Seeker <algorithm AT gmail DOT com> wrote:
> > > I have searched the list and last postings were in Dec 2002. I
want to
> > > backup a snapmirrored volume (the destination) using NDMP. Do I
have
> > > to use the snapshot from the volume or there exist any better
options.
> > >
> > > Also is there any body who is successful in doing a snapmirror to
tape option?
> > >
> > > Thanks
> > > _______________________________________________
> > > Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
> > > http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu
> > >
> >
> > --
> > -Tim
> >
> 


-- 
-Tim
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