What-What?? What Is Going On With This Snapshot?!?
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- We can continue working with the original device, without changing the
data in the snapshot.
- COW (Copy-On-Write) - Every time data is written to the original device,
the Linux kernel copies the old data to the snapshot's device, and only
then updates the original device.
- Thus, the first write to a snapshot is translated into a read (from the
origin), a write (to the snapshot) and another write (to the origin).
- The kernel keeps an on-disk hash-table of the chunks that were copied
to the snapshot.
- This is used both for reads, and to avoid redundant copies.