Guest image as Immutable or Writethrough - image protection?

[suzubivuw]

I discovered quite interesting feature of VirtualBox which I most likely will put in good use - changing the Guest image from "Normal" to Immutable or Writethrough" It appears this and creating snapshots is quite good way to prevent corruption of your Virtual Images. (and more convenient than creating backups or clones of the Images). ...

Thoughts?

[scottgus1]

It appears this and creating snapshots is quite good way to prevent corruption of your Virtual Images. (and more convenient than creating backups or clones of the Images)

Respectfully, Suz, neither of these statements are true, and either function will leave you out dangling in the breeze one day if you depend on them for backup and corruption-prevention.

Snapshots make a guest more delicate and do not work as backups. They are similar to Windows' System Restore points: point-in-past-time markers, not extractable, useless without the base system in place, but easier to corrupt because the files are accessible on the host drive. They should only be used on guests you're experimenting with and with data you wouldn't mind losing. (The forums are replete with users destroying their important data because they did something wrong with a snapshot.)

Additionally, each snapshot, if used long enough, has the potential to grow to the final size of the original drive, and will not shrink once another snapshot is taken. The guest's total data size on the host could be many times what it would have been without the snapshots, and with tremendous amounts of dead data that will never be used or changed.

The best backup is a simple folder-copy after the guest is shut down. See this tutorial Moving a VM and re-interpret it as "Backing Up a VM".

Of course you could also get in-the-guest 3rd party backup software, which can image the guest while it's running to a host shared folder and may be able to do incremental backups.

BTW, some folks think using the Export function is a backup process, and you mentioned cloning. Exporting and cloning are not recommended for backing up a VM. Either process changes some guest settings, and Export tries to match the older OVA format and is intended for using a guest under another hypervisor besides Virtualbox. A change in the guest means there's no way to confirm the backup. Backing up with the "Moving a VM" method allows a simple FC file compare for backup confirmation and is compatible with encrypted guests.