You have taken a Logical Volume Manager (LVM) snapshot backup of a volume that contains the MySQL data directory. Why is it important to remove snapshots after completing a raw backup in this way?

The correct answer is C. The snapshots take a significant amount of disk space because they are a duplicate copy of the data. Note: The provided answer key appears to contain an error. Option A is the technically correct answer for LVM snapshots, not C. LVM snapshots use a Copy-on-Write (COW) mechanism - they do not start as a full duplicate of the data. Instead, as blocks on the original volume are…

Backup and Recovery

Question

You have taken a Logical Volume Manager (LVM) snapshot backup of a volume that contains the MySQL data directory.
Why is it important to remove snapshots after completing a raw backup in this way?

Options

AThe snapshot size will continue to grow as changes to the volume are made.
BThe system can only support one snapshot per volume, and you need to remove it to be able to take your next backup.
CThe snapshots take a significant amount of disk space because they are a duplicate copy of the data.
DThe system keeps a copy of changes in memory and can cause an out-of-memory event.

How the community answered

(25 responses)

A
4% (1)
B
4% (1)
C
92% (23)

Explanation

Note: The provided answer key appears to contain an error. Option A is the technically correct answer for LVM snapshots, not C.

LVM snapshots use a Copy-on-Write (COW) mechanism - they do not start as a full duplicate of the data. Instead, as blocks on the original volume are modified, the original block is copied into the snapshot before being overwritten, causing the snapshot to grow over time. If the snapshot's allocated space fills completely, it becomes invalid and unusable, which is the primary reason to remove snapshots promptly after a backup is done.

Why each option is wrong (or misleading):

A (actually correct): As writes occur on the live volume, the snapshot accumulates original blocks via COW. Unremoved snapshots eat into volume group free space and risk invalidation.
B (wrong): LVM supports multiple simultaneous snapshots per logical volume.
C (marked correct, but misleading): Snapshots are not a full duplicate copy - that's the whole point of COW. They start near-zero in size and grow only with changes.
D (wrong): LVM snapshot metadata is tracked on disk, not in RAM; this is not a real risk.

Memory tip: Think of an LVM snapshot as a "change journal" - it only records what was there before each change. The longer the volume is in use after the snapshot, the more it fills that journal. Take backup → remove snapshot → free the space.

Topics

#LVM snapshots#backup storage management#snapshot lifecycle#disk space implications

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