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nirvimel2017-04-09 20:30:31
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nirvimel, 2017-04-09 20:30:31

Is there a virtualization technology that allows the use of "decremental" snapshots?

VirtualBox, for example, uses incremental snapshots, when, after creating a snapshot, the contents of the disk itself are "frozen" and all changes are written to the snapshot file, when the snapshot is deleted, all changes are reset to the disk (a lengthy operation), and when rolled back, the snapshot file is simply deleted ( instant operation).

I'm interested in a technology with the opposite approach, when all changes are written directly to disk, and the previous contents of the changed sectors are written to the snapshot file, then snapshot rollback becomes a lengthy operation (all changes on the disk are restored from the snapshot file), and deletion is instantaneous (just deleting the file ). Let's call this a "decremental" snapshot (as opposed to incremental).

What is it for:
For virtual disks (images), the only difference is the speed of delete and rollback operations, but for physical disks it makes a lot of sense. You can enter a physical disk in a virtual machine (with valuable data, for example) into any state, perform any risky operations on it (repartitioning, etc.), and then, depending on the results (all_normal or all_missing), or leave disk in this state, or roll back all changes.

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2 answer(s)
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Rsa97, 2017-04-09
@Rsa97

Windows Volume Shadow Copy uses copy-on-write by default.

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Puma Thailand, 2017-04-10
@opium

No, of course, then the snapshot would take hours, and on large systems for days, who needs it.

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