What Is A Snapshot?

• 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.

Originally written by guy keren