Disk snapshot

From Wikipedia, the free encyclopedia

In data storage, a disk snapshot or "Point in Time Copy" is a copy of the state of a storage device at some instant in time.

Its primary purpose is to reduce the "backup window" to zero time, to eliminate the dilemma caused by simple "full backups": A full backup to tape may take hours.

  • If users are allowed to access that storage during a full backup, the backup tape might contain files in an inconsistent state. For example, if a user moves a file into a directory that has already been backed up, from a directory that has not yet been backed up, that file would be completely missing on the backup tape.
  • To prevent that problem, administrators may take the storage device offline during a full backup. Users get annoyed when they cannot access their data for hours.

A snapshot takes (effectively) zero time.

  • Users can read and write files as normal to the "original copy" before and after the instant of the snapshot. The "snapshot copy" can then be used for a full backup to tape or a virus scan.

Snapshots are a common function found in enterprise storage and RAID devices.

A disk snapshot (unlike a mirror) is typically implemented using links between the original (or source) and the copy (or mirror).

[edit] External links

Retrieved from "http://en.wikipedia.org../../../d/i/s/Disk_snapshot.html"