I've been playing with the new
Imagine a large 10TB disk. A snapshot, that may last for an hour, may be lucky to see 100GB written to it, yet it would have the full 10TB allocated for each snapshot.
If the underlying storage (iSCSI) is thin-provisioned you can just massively over-provision each volume, though that may look ugly on that side if everything is over-provisioned by a factor of two. Might I suggest two options that may go some way to reducing this problem:
Snapshots as Volume-Chain feature. It works fine, but I've noticed that for each snapshot it creates a snapshot volume that is the same size as the source volume. I suppose this make a certain sense, and may even be a hard requirement, but it does pose a problem for large VM disks, since it implies that the underlying VG has free space at least as large as the largest volume, no matter how little writing will actually happen while the snapshot is present. For large VMs may be very large indeed.Imagine a large 10TB disk. A snapshot, that may last for an hour, may be lucky to see 100GB written to it, yet it would have the full 10TB allocated for each snapshot.
If the underlying storage (iSCSI) is thin-provisioned you can just massively over-provision each volume, though that may look ugly on that side if everything is over-provisioned by a factor of two. Might I suggest two options that may go some way to reducing this problem:
- Allow a second, large, VG to be specified to be used for these snapshot chain volumes.
- Allow a size to be specified (% or absolute) for the size of the snapshot volume to be created. Granted, there would be a risk here of filling this snapshot if this was set too low, or the snapshot kept too long.