Hm... this is good one. VTL is good because you create multiple small volumes which you can assign to small LUNs thus you get good performance. If cloning make sure that volume is not big because that can cause some issues. Bad thing is that it emulates tape thus we get to disk advantage which gives you chance to read and write at the same time from the same volume. One thing that I hope to see soon are multiple reads from the same volume. Having disk solution also assumes you will need to stage data unless your disk capacity will be able to keep you data for your retention. This leads to another advantage point in favor of CDL which is compression. While you can have compression on application level, I would not go down that path. On the other hand I'm very pleased with compression I have seen with few EDL products I have worked with.

We are attempting to size the environment to hold our normal rotation of backups - as such we are very concerned about wasted space. My biggest VTL concern is the "trapped" space you can get from having only part of a fully utilized tape "unexpired" but full of say 400GB of data.

Does Networker have the ability to "defragment" tapes to avoid this scenario?

The lack of compression on raw disk storage for backups definitely is a big negative and one "feature" I was not aware. I believe (at least the sales people told us this) that there is a de-duplicating storage agent coming out which will provide some "compression" to front-end disk storage I guess.

No. NW does not defrag tapes as tapes are entity under library control (in this case CDL). You could stage data but that would be unnecessary overhead and operation without much sense. On the other hand if you use advanced file device then expired ssids are removed.

So in reality CDL will compress and disk device will remove expired ssids and at the end, depending on your backup cycle and policies you may get the same thing. Not sure how much same this is from license point of view.


Exactly, that's integration of Avamar with NW which is next big thing hitting shelves.