Local storage - lack of space for backup snapshot?

[StuartLittle]

Hello All,

Apologies if this is an obvious question but I was wondering if anyone could shed any light onto a question I have regarding our ESXi server.

We run ESXi on a Dell PowerEdge 1950 III with 16GB Ram and with 200GB RAID 5 15K RPM SAS for the local storage - we don't have a requirement for a SAN etc and I understand the "best practice" way of setting up ESXi and that local storage is not advised.

Our question is:

We are currently running very low on the amount of local storage space on the server and we use a Perl script every night to create a snapshot of only the one VM we want to back up which copies the original VM files to a seperate NAS device. Apart from slow performance this setup works well for us. However, during the course of the backup the snapshot file obviously grows with the delta changes that are made and once the backup finishes it writes these changes back to the original vmdk file (or so I believe). Can anyone say what would happen if we successfully created a snapshot at the start of the backup but the server ran out of space before the backup finishes and comitting the snapshot changes ... would this seriously damage our original server vmdk ?

If you need further info on our setup please let me know but I would appreciate any advice before we embark on this ... thanks in advance.

Stuart Little

[admin · Accepted solution]

If the volume runs out of space while you have an active snapshot on a VM it will stop running (the VM will crash) and you will not be able to commit the snapshot (free space is required for this). Always avoid the chance of filling a volume especially if you are using snapshots, while you probably won't lose data if you handle it correctly (move the VM to a volume with storage, or free some space before trying to commit the snap) you will have VM downtime at the very least.

Alex

www.phdvirtual.com

[StuartLittle]

Hello Alex,

Thank you for the quick response and explanation. I will make sure to free up enough space on our existing Datastore to ensure the backup completes and the snapshot can commit to the VM. The problem I have is trying to determine how much data will be written to the snapshot over the backups duration (12 hours) - at the moment there is approximately 4.5GB free space and when we create a new snapshot it automatically allocates the servers memory size i.e. 2GB which leaves us with only 2.5GB of free space that can be written to while the backup is running ... should hopefully be enough.

Thank you again for your time and advice.

Kind regards,

Stuart Little