How VMware snapshots affect Veeam backup efficiency?

Recently I was given task to take over one VMware environment which has Veeam backup in use. When going through the environment, I found out that some backup jobs take way more time that what I have usually seen and started investigating this issue.

First thing that I found was, that there are lot of snapshots in that environment, also in those servers that are backed up with Veeam. Little search at Veeam's Forums and I found this topic: http://forums.veeam.com/veeam-backup-replication-f2/can-snapshots-slow-down-running-backup-t22521.html

So, it's quite obvious, if you have snapshots on those VM's that you are backing up with Veeam, it will slow it down because consolidation is slower with nested snapshots. (So, backup itself is still fast, but 'cleaning up' after backup is slower)

But, is it really that much slower?

I had to follow the situation for a while since I was quite curious to see that how big impact does snapshots have. And the impact, it's way bigger than what I suspected.

This table shows impact of removing snapshots from VM's:

VM	Snapshot size in GB	Average time to do consolidation with old snapshots	Average time to do consolidation with just Veeam snapshot
Machine 1	9	1 minute	15 seconds
Machine 2	78	30 minutes	30 seconds
Machine 3	8	2 minutes	under 10 seconds
Machine 4	25	12 minutes	under 10 seconds
Machine 5	16	2 minutes	under 10 seconds
Machine 6	31	10 minutes	under 10 seconds
Machine 7	4	1,5 minutes	15 seconds
Machine 8	87	30 minutes	under 10 seconds
Machine 9	34	15 minutes	under 10 seconds
Machine 10	23	10 minutes	under 10 seconds

Conclusions? Don't keep snapshots on your environment if you don't need them, it will slow down things. And this is just one thing that it slows down, it of course affects to VM performance also, but there are lot of good blog articles about that already. With only 10 VMs, time saved with just removing old snapshots was almost 2 hours. You can just imagine that how much time you can save in you backup jobs if you have ten's or even hundreds of VMs that have (forgotten) snapshots.

And of course, impact is also dependent on your overall storage performance. In this case, underlying storage is quite reasonable, so with slow storage, impact might be even bigger.