Veeam takes time to backup empty space..?

[mdornfeld]

Hi all,
As I was watching my Veeam backup job (v3.1) go through a 500 GB Virtual RDM it came to my attention that the Veeam backup job wrote all 500 GB's at the exact same speed, even though I only have 50 GB's of data on that Virtual RDM. So it appears as though Veeam just spent a lot of time writing a lot of zero's. I'm pretty sure, but not certain, that this copying of empty space also applies to your standard thick .vmdk disk file.

I suspect this is happening because Veeam uses the vcbmounter.exe "-F 1" option, which tells VCB to transfer all the data as a flat file, and do no compression.

Can anyone else confirm these findings? Is there anything that Veeam can do about this?

Thank you.

[Gostev]

Matt, the vcbmounter.exe "-F 1" option is required to fetch bit-identical copy of the source VM, unlike default "-F 0" option that fetches sparse file. Veeam Backup needs bit-identical copy to be able to calculate incremental changes for subsequent passes, leverage synthetic backup, and perform instant file-level restores from backup. Previous versions of ESX server (until ESX4) simply did not provide any other methods for determining VMDK changes, so we have to do this on our own. ESX4 does provide change tracking functionality, but you are on ESX3.5 anyway as far as I remember.

However, while Veeam Backup will indeed read whole VM (500GB), it does not spend time writing zeros as you assumed. Veeam Backup will drop all empty blocks on-the-fly (so zeros are not hitting the disk), and compress/dedupe the remaining blocks which contain actual data.Theoretically, if there is indeed only 50GB of data in vRDM, your backup size should be smaller than 50GB. If you are not seeing this, you should perform defrag&wipe of your vRDM disk.

Hope this helps!

[mdornfeld]

Thanks Gustov. I am on 3.5, and my backup size is smaller then 50GB. I'm seeing from your post that there's nothing you can really do to read blank data faster in my version because of the bit-identical copy.

Has Veeam been able to take advantage of the added functionality in 4.0 that you mentioned to dramatically increase backup times? If not yet, will we see something in a nearterm future release?

Thank you again.

[Gostev]

Yep, actually this stuff already works in current Veeam Backup 4.0 builds... 30 sec for incremental backup of 100GB VM, pretty major improvement there comparing to current version numbers But again, this functionality would require ESX4 hosts, anyone with previous ESX versions will have to do it the "old way". Thanks!

[mdornfeld]

Thanks Gustov.

Quick clarification, are you saying it currently works in the Veeam 3.1 build, or it's going to work in the Veeam 4.0 when it's released? If it's Veeam 4.0, when do you expect Veeam 4.0 will be released?

[Gostev]

No, I am talking about current Veeam Backup 4.0 builds, to be released late Q3.