On 05/14/2016 02:38 AM, Greg Padgett wrote:
On 05/12/2016 03:46 AM, SATHEESARAN wrote:
Hi All,

I have created a VM with 60GB of disk space.
I have started I/O inside the VM, after sometime when the disk was 4GB full,
I took a snapshot of the disk from UI.

I/O kept continuing and the new image file ( overlay file ) was 15GB in

Now I deleted the snapshot.
I think this would initiate block-merges.
During this time, my I/O was were slower, till the snapshot delete is

Its not very slow, but slow.
Is this a known behavior ?

Hi Satheesaran,

It sounds like this was a live merge, ie snapshot removal while the VM was running. This is currently implemented as a block commit, where data from the snapshot (your 15GB overlay, in this case) is merged down.

For snapshot deletion to complete, this means that your concurrent I/O and the data already in the overlay have to be written into the next-lower image. So in short, yes, depending on the storage system backing your VM, I/O may slow down a bit until completion.


Thanks for that information.
I too expected it, but really wanted to confirm the behavior.

-- Satheesaran S
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