Very slow snapshot deletion

Discussion in 'Parallels Desktop 15 for Mac Technical Preview' started by KorkyPlunger, Jul 31, 2019.

  1. KorkyPlunger

    KorkyPlunger Kilo Poster

    I have a fairly large VM (~475 GB without snapshots). It had one snapshot in it from around 2 months ago, so I attempted to delete it because it had grown to around 580 GB.

    The deletion process has been running for at least 3 hours already. This seems painfully slow, more than I remember with older versions. Some things I noticed:
    • There's very little disk activity going on. It seems to be in small bursts. Watching the file size of the .pvm file, it drops by 120 MB every 15 to 30 seconds which seems quite slow... only around 14 to 28 GB per hour?
    • There's very little CPU being used. All other apps are idle, and the prl_disp_service process is using 100% of a single core. Could this could be parallelized to take advantage of all 6 cores I have available?
    • No progress is shown on the "deleting snapshot" window. The bar has been at 100% complete (with a shimmering effect on it) the entire time, which makes it hard to gauge progress.
    I have filed Technical Data while the deletion process was running, report #318873274

    Is there any way to speed this up, other than to not use snapshots?

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  2. KorkyPlunger

    KorkyPlunger Kilo Poster

  3. SterlingG

    SterlingG Bit Poster

    For what its worth .. I have always found that using the 'native' snapshot facilities in a virtual machine (for example btrfs or apfs) to be faster than using a snapshot facility provided by a VM manager. This applies not only to PD15, PD14...etc but also VMware and Virtualbox. Long ago I asked which was preferred (on these very Parallels forums) and never really got a clear answer. I suspect your slow removal of a snapshot is a lot of "follow chain of changed blocks, move change to the 'home' for it, get next chain".

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