- A snapshot is an operation in which we “freeze” the data on a logical volume, while still enabling writing new data.
- This, of-course, is an oxymoron.
- It is solved by splitting the data to old (written before taking the snapshot) and new (written after taking the snapshot).
- The old data resides on the original logical volume.
- The new data is written to a different disk.
- When an application reads from the device, the underlying kernel code finds where lies the fresh copy of the data, and returns that to the application.
- Meanwhile, we may mount the original (frozen) content on a different directory, and access it in read-only mode.
- E.g. to backup the data.