Opened 5 years ago
Last modified 5 years ago
#19541 new defect
Poor disk write performance for fully allocated sparse-extent VMDKs
| Reported by: | vorteil-alan | Owned by: | |
|---|---|---|---|
| Component: | virtual disk | Version: | VirtualBox 6.1.6 |
| Keywords: | Cc: | ||
| Guest type: | other | Host type: | all |
Description
Using sparse VMDK disk images, VirtualBox's disk write performance drops dramatically if the "sparse" image is fully allocated. This was surprising and unintuitive since we figure that using a sparse image is meant to be a tradeoff where we sacrifice performance in exchange for a smaller file size.
I've attached two 4GiB VMDKs. Both are completely empty and both are technically sparse-extent VMDKs, but one is 100% pre-allocated and the other is 100% unallocated. If you attach these VMDKs as second and third disks to an Ubuntu VM running on VirtualBox and measure their write performance (using dd to write to /dev/sdb and /dev/sdc, for example) the difference in write speeds is clear.
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Here's a link to the zip archive I mentioned. I couldn't attach it to the first post due to its file size.
https://drive.google.com/file/d/1tt38VgF5iIKdxIA3FQZcs64xFIJKsUF2/view?usp=sharing