Prl-disk-tool for Virtuozzo 7

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1. Feature

prl_disk_tool for Virtuozzo 7

2. Description

The package prl-disk-tool (binary /usr/sbin/prl_disk_tool) is used to manage virtual machine and container disk images can perform the following operations:

1. resize --size ... : Resize image (in-place)

2. resize --size ... --resize_partition : Resize image and last partition to fit (copying)

3. resize --info : Display resize estimates (current size, minimum size, minimum size w/o resizing last partition) - VM only

4. compact : Compact image to occupy less space on host disk. (in-place)

5. compact --info : Display compact estimates (block count, allocated, used) - VM only

6. merge : Merge internal snapshots of image (in-place) - VM only

7. merge --external : Merge external snapshot of image (in-place) - VM only

8. convert [--plain | --expanding] : Convert image between plain and expanding modes (copying) - VM only

prl_disk_tool uses libguestfs, qemu-img to work.


The user has to install additional packages to use part of functionality:

  • prl-disk-tool resize --info (last partition: btrfs) → btrfs-progs >= 4.2 (already in repo)
  • prl-disk-tool resize {--info,--resize_partition} (last partition: ntfs) → libguestfs-winsupport (already in repo)
  • prl-disk-tool compact {--info,} (exists partition with ntfs) → libguestfs-winsupport


prl_disk_tool locks an image passed as argument by flock(). So only multiple reads ({compact,resize} --info) OR a single write (others) are allowed.


FS-aware functions (resize {--resize_partition|--info}, compact [--info]) work for ext2/ext3/ext4/ntfs/btrfs/xfs.

prl_disk_tool uses qemu-img to perform fs-unaware operations. It is more powerful than qemu-img due to fs-aware operations performed with libguestfs.

The main purpose of prl_disk_tool is to automate some frequent operations.

3. Products

Virtuozzo 7 beta2

Packages:

  • prl-disk-tool >= 7.0.5
  • libguestfs >= 1.28.1-1.18
  • btrfs-progs >= 4.2 (optional)
  • libguestfs-winsupport >= 7.2.1 (optional)
  • libguestfs-xfs (in dependencies)
  • qemu-img >= 1.5.3-86

4. Testing

Need to test the following cases:

  • All functions work for qcow2 images.
  • Functions not tagged as VM only work for ploop images.
  • FS-aware functions (resize --resize_partition|--info, compact [--info]) work for ext2/ext3/ext4/ntfs/btrfs/xfs.

5. Known issues

  • resize --resize_partition should be implemented in-place (due tolimitations of qcow2, only for expanding)
  • all modifying operations have --dry-run option to not modify an image. The image is still opened for write, and exclusive lock is acquired.
  • only listed filesystems are supported
  • virt-resize, used by resize --resize_partition, leaves an empty block of ~3M at the end of image.
  • convert --plain fallocate()s space inaccurately (due to unawareness of qcow2 internal structures).
  • resize [expand] after convert --plain does not force allocation of new (bigger) chunk of space (we do not keep image type (plain/expanding) for now - so it is impossible to determine whether we should allocate space outside of convert operation)
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