VTL vs disk backup

Question

We are looking at a possible option to bring-in Networker to replace an existing backup product (FDR Upstream) and are basically in the position to architect the solution from the ground-up. As such we are trying to make replicated disk the core of our backup infrastructure with tape being used only for long term archiving needs.

My question being that I have no real experience with Networker - is given the choice between using a VTL (such as the EDL) or raw disk solution (cheap drives on say a Clariion) which would you opt to use? I have some experience with the CDL using Data Protector software and realize some of the inefficiences with managing tapes on storage.

Which option would you choose at what big gotchas do you see with either solution?

ble1 · Answer

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.

bodnarg · Answer

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.

ble1 · Answer

Does Networker have the ability to 'defragment' tapes to avoid this scenario? 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. I believe (at least the sales people told us this) that there is a de-duplicating storage agent coming out which willprovide some 'compression' to front-end disk storage I guess. Exactly, that's integration of Avamar with NW which is next big thing hitting shelves.

NetWorker

VTL vs disk backup

Was this post helpful?