On 20/08/2008, at 9:21 AM, Curtis Preston wrote:

So an AFTD can service multiple concurrent restore requests, but can't service multiple destaging/cloning requests?

Yes.

I still say the VTL is easier. The difference is that a backup associated with a given AFTD can only be cloned/destaged by the AFTD that stored it, where a VTL allows any-to-any relationship of virtual drives.

If I have 20 virtual tapes and 20 virtual drives, I can clone/ destage them all at once, regardless of how many drives were used to create them. If an AFTD can only clone/destage one backup at once, and I want to be able to destage 20 AFTD backups, I have to make sure that each of them is on a separate AFTD. I don't think that's even possible, let alone practical.

Am I missing something?

Cheers,

Preston.

-----Original Message-----

From: EMC NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On Behalf Of Preston de Guise

Sent: Tuesday, August 19, 2008 3:48 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: [Networker] Query in Staging from adv_file

On 20/08/2008, at 8:35 AM, Stan Horwitz wrote:

On Aug 19, 2008, at 6:16 PM, Curtis Preston wrote:

Well, that significantly decreases the value of AFTDs over VTLs in
NetWorker, now doesn't it?

I have no experience with a VTL, but my impression is that you get
the same functionality as physical tape drives, but on disk. If so,
doesn't that limit the amount of streams that can be read from a
virtual tape to just one session at a time, or does it parlay the
fact that multiple local tapes can be serviced concurrently in a VTL?

In theory it doesn't make AFTDs any worse than VTLs, since neither
scenario supports more than one staging operating reading from the
same volume at the same time.

However, in practice VTLs will normally be configured such that there
are a high number of virtual tape drives and a high number of smaller
sized virtual volumes, making it possible to execute more concurrent
reads than either a conventional PTL or a AFTD.

I wouldn't however say that it significantly decreases the value of
AFTDs over VTLs in NetWorker - it entirely depends on what your needs
are. In an environment that requires high levels of recovery
activities, AFTDs may still win out over VTLs - e.g., a previous
customer of mine had a configuration that required 400-600+ recoveries
per working day (i.e., an 8 hour period each day); in this sort of
scenario AFTDs with their ability to allow as many concurrent recovery
sessions as requested are of course King.

Cheers,

Preston.

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