vhd-tool

Command-line tools to manipulate, transcode and stream vhd format data.

Basic command-line tool examples

To create an empty dynamic (i.e. grows on demand) vhd:

vhd-tool create filename.vhd --size 16GiB

To create an empty difference vhd:

vhd-tool create filename.vhd --size 16GiB --parent otherfile.vhd

To query all the parameters of a vhd:

vhd-tool info filename.vhd

To query a specific parameter:

vhd-tool get filename.vhd current-size

Example: incremental backup

(This is a work in progress)

When running VMs on a hypervisor like XenServer, it's important to have a backup strategy for your important virtual disks. One possibility is to perform periodic disk snapshots and archive the "deltas" (or differences) between the new snapshot and the last.

First take a snapshot: this will be the first backup:

xe vdi-snapshot uuid=<uuid>

Next download the snapshot as a single .vhd:

xe vdi-export uuid=<uuid>

This will print a filename to the terminal.

Periodically (e.g. from cron), perform a new snapshot:

xe vdi-snapshot uuid=<uuid>

Next download the differences from a previous snapshot as a single .vhd:

xe vdi-export uuid=<uuid> relative-to=<previous-uuid>

Next, to avoid using too much disk space, count the number of snapshots and delete the oldest if you have too many:

xe vdi-destroy uuid=<oldest-uuid>
vhd-tool commit filename.vhd --into older.vhd

To restore a backup onto a fresh system use:

vhd-tool stream --source filename.vhd
                --source-format vhd
                --destination http://user:password@xenserver/import_vdi
                --destination-format vhd
                --progress