In a multi-storage-node environment, you will need to do a lot of
provisioning and management that you simply don't have to do in the VTL
world.  You have to figure out how big each AFTD must be, slice them up,
then divvy them out using zoning and LUN masking.  Making them too big
minimizes performance.  Making them too small increases management.
Then when you need more, you have to add more, and you have to
reconfigure your backup environment each time.  You just don't have
these issues with a good VTL/IDT.

Then there's the NW issue that a single backup can't span an AFTD.  (I'm
sure they're working on that one.  Symantec just added this to NBU, so
it's a common problem.)

As to NW's ability to read and write AFTDs simultaneously, it's not
something that really excites me.  It allows you start cloning each
backup as soon as it's done, but you're going to have to script that.
AND, if you make your virtual tapes 100 GB in size, you can fill one up
in 30-60 mins with a transfer rate of 50-100 MB/s.  So you have to wait
an hour before starting to clone each tape -- I don't see how that's
going to impact anybody.  If you're asynchronously copying the tapes as
they're filled, then this will cause a 1-hour delay at the beginning,
but nothing the rest of the night.

---
W. Curtis Preston
Backup Blog @ www.backupcentral.com
VP Data Protection, GlassHouse Technologies 

-----Original Message-----
From: Teresa Biehler [mailto:tpbsys AT rit DOT edu] 
Sent: Thursday, August 23, 2007 5:28 AM
To: EMC NetWorker discussion; Curtis Preston
Subject: RE: [Networker] new to Virtual Tape Library - what are the
benefits?

Curtis,

Could you comment on what you see is the problems with AFTD in large NW
environments?  You mentioned them in this item, but don't go into
detail.

Thanks.
Teresa

-----Original Message-----
From: EMC NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On
Behalf Of Curtis Preston
Sent: Wednesday, August 22, 2007 7:36 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: [Networker] new to Virtual Tape Library - what are the
benefits?

I've read this whole thread now and wanted to comment on it with a
little more thought...

.
.
.
2. There's also the issue where you can't expire a tape until all its
backups expire.  This is no different than physical tape.  I think this
is pretty easy to deal with.  Either use really small virtual tapes or
mark your tapes as full with a script after each night's backups.  A 400
GB tape marked full in a VTL won't take up 400 GB, so that's OK.  That
way, each night's backups are on their own set of tapes, causing all of
them to be expired when those backups expire.  (You also need to
segregate by retention period if this is to work well -- just like with
real tape.)  You don't have this issue with an AFTD as it can expire
individual savesets, but I think that an AFTD comes with too many other
problems in large NW environments.

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