> Actually current filesystems do pretty well on thinly provisioned > storage, as long as your extent size is not too small. Starting from > extent size in the 64M to 256M range there's almost no difference to > non-virtualized storage. > > Again, sparse images with a large enough allocation size give you almost > the same numbers as preallocated images. I've been doing quite a lot of > work on TP support in QEMU. Using an XFS filesystem to back the image > with an extent size hint in the above mentioned range gives performance > withing 1% of fully preallocated images. With the added benefit of > allowing to deallocate the space again through the SCSI WRITE_SAME > or ATA TRIM commands.
These numbers are very interesting and I would like to read more. Are your detailed results accessible on the Internet? Do you have numbers on the impact of using a large extent size (64-256MB) on thin provisioning (since a guest file system's metadata are written first and are scattered in the virtual disk)?
