Flashbackup Full vs. Differential behavior (full disk vs. deltas)

[Georges_N]

Hi guys

thought I'd start a little discussion on something that's been bugging us here at my company.

Setup:

File server with multiple disks. One in question is 8TB, with about 4TB used.

If we run a FULL FlashBackup-Windows, it'll backup the whole 8TB disk (half full half empty) and take the same time it'd normally take for 8TB of data anyways.

When running an incr-diff backup, it will take the deltas only (so around 30-80gb a day depending on the day) - how does it do that? What we're trying to accomplish without modifying anything on the file server itself is take the backed up files only, not the empty disk space.

What are we doing wrong?

File server = Windows 2008 R2 x64

Master NBU server = Windows 2008 R2 x64 - NBU 7.5.0.6

Policy = FlashBackup-Windows (although we've run tests on different disks using MS-Windows policy and it takes the full disk too)

Is it the type of disks we're using? We're using RDM disks for our file server and a VMDK for the test... same result.

Not sure if I'm super clear on this - btw this is just a discussion not something I'll raise with Symantec. Just trying to get an idea from the community...

Thanks

[RamNagalla]

as you are having netbackup  7.5.0.6 and you are testing the VMDK, 

could you try using the policy type as VMware.. in this policy type you do have the option "Exclude deleted blocks" where it will not take the empty blocks..

[Mark_Solutions · Accepted solution]

When you run a Full backup using FlashBackup-Windows it does a block level backup of the drive and so backs up the entire drive regardless of how much free space it has on it - data is irrelevant, it just backs up the blocks

When you do an incremental it backs up the changed blocks - so this may still be larger than the actual data change as it backs up all blocks that have changed data on them

It is just the way it owrks i am afraid

As Nagalla points out a VMWare backup has a little more functionality but not much

With Flashbackup it is best to not have too much free space if possible for exactly this reason

The only thing i can think these days that would improve things for you would be to use accelerator - first backup would be horrendous but after that it would work well for you.

Hope this helps and explains a little about how it works

[Nick_Morris]

As Mark says, Accelerator is your best bet if you have the necessary storage/licenses to do that. 8TB wouldn't work well with a VM as it's too big to do a snapshot backup of and RDM don't usually get snapshotted in vCenter. Another option if possible is to use a smaller drive and have it around just 75-80% full (e.g a 5TB drive if only 4TB used), though i know that can be too tricky and long winded to do in most situations, though it's another option.

[Georges_N]

Thanks Nagalla - would have been a good one if it allowed to specify a drive letter (it only accepts "all local drives" which would take forever)

The "almost full" drive is what we had before - we archived our file server so around half the data is now gone. Shrinking the disks is going to be a pain but it looks more and more like our only option....

[RamNagalla]

you do have a option to exclude boot disks or data disk... but not specific disk..

and this is on policy-->VMware tab---> Advanced  if it helps you... 

[Georges_N]

Thanks, I noticed a few new options to play around with but nothing came up with a positive result - I believe I'll open a case with Symantec to double check what could be wrong.

Thank you