Best practice for snapshot space reserve

[wade001]

We create datastores with 10% + Memory as reserver area for holding snapshots and suspended state information, We have had issues with performing Veeam backups of a SQL VM server due to the snapshot file gorwing huge and running the datastore out of space. We believe the issue was a result of a maintenace job to perfomr flatfile backups occuring at the same time Veeam runs. We are now looking to use Veeam to protect a rather large Exchange server (1,300 users) and are concerned the backup proccess creating snapshots may run our deadicated datastore out of space during this window We would rather not deadicate a large reserve of free space just to accomindate the nighlty Veeam / Snapshots task and are looking for some guidelines in this regard ie best practice for VM snapshot reserve any ideas on hoe to try and calculate this requierment??? Our EX servers are nearly 200 GB in size and the initial Veeam backup completed in a little over three hours...

[donikatz]

I assume you mean 10% disk space free, not memory. As you've found, 10% is often not nearly enough for large snapshots. A busy database like Exchange can generate very large delta files during the snapshot process, depending on how many transactions, since all new writes go to the delta file. This has nothing to do with Veeam, everything to do with VMware snapshots. The basic rule of thumb of keeping 20% disk free can be way off your real-world needs; only you can figure out how much you'd need, which is again based more on your disk write change activity than on base VMDK size. I would recommend taking a regular VM snapshot during your expected backup window and seeing how quickly it grows. Based on that and how long it takes your Veeam backup job, you can extrapolate how much extra disk space you'll need.