Disk space requirements for backups and snapshot

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Alessandro 123

Well-Known Member
May 22, 2016
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As subject, how many free space we need for backing up (live) a VM or for taking snapshot over a gluster storage and over a ZFS filesystem?

I'm asking this because in xenserver a snapshot require at least the same space used by VM disk (a 200gb VM, with only 1gb used, requires 200gb free to take a snapshot) and a snapshot is required for taking online backups.

What about proxmox?
 
It depends on your disk configuration.

If you set the discard option and your vm os supports it, the underlying storage like zfs will free the unused blocks. In this case your snapshot size will be equal to your used space in your vm.

regards Nicolai
 
Let's assume a VM without "discard" option set.
The VM is 200GB, but with only 10GB used.

Now I want to take a snapshot. Do I need 200GB to create the snapshot?
Now I want to take a backup with running VM. How many free space do I need?
 
"up to" or, like with xenserver, "at least" ?
In xenserver you can't create a snapshot if you don't have at least the same space available
 
If you take snapshot with lvm or zfs the initial snapshot will be very small. It grows while the original image is further used - but the growth depends extrem on the knowledge of freed blocks. So if you take a snapshot and copy the data to another location for backup purpose and remove it afterwards it will be fine and would not need much additional space. If you want to keep your snapshots you have to keep in mind, that the snapshot may grow to the original image size.
 
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