What is the guideline for the size of an LVM snapshot volume on RHEL?

Solution Unverified - Updated -

Issue

  • We are migrating / backing up a file system. The process is: 1) add SAN disk B, 2) snapshot disk A, 3) copy  content from the snapshot to B, and 4) remove the snapshot.
  • How should the snapshot size needed be estimated?
 Man page for lvcreate says for snapshot: "The snapshot does not need the same amount of storage the origin has. In a typical scenario, 15-20% might be enough." Is this 15-20% guideline assuming the snashot was not taken for read-only purpose? If snapshot taken for read-only purpose, do i still need 15-20% storage space as the origin has? In this case, what is the guideline for the percentage? Would 100M enough for snapshoting a 2 T file system?

Environment

  • Red Hat Enterprise Linux 4+ (RHEL4+)
  • Logical Volume Manager (LVM)

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