Copy-on-write: Difference between revisions

Revision as of 00:54, 27 May 2022

Revision as of 03:13, 1 June 2022

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==In computer storage==

COW may also be used as the underlying mechanism for [[Snapshot (computer storage)|snapshots]], such as those provided by [[logical volume management]], file systems such as [[Btrfs]] and [[ZFS]],<ref>{{cite web|url=http://sakisk.me/files/copy-on-write-based-file-systems.pdf|title=Copy On Write Based File Systems Performance Analysis And Implementation|last=Kasampalis|first=Sakis|year=2010|page=19|access-date=11 January 2013}}</ref> and database servers such as [[Microsoft SQL Server#Replication Services|Microsoft SQL Server]]. Typically, the snapshots store only the modified data, and are stored close to the main arrayoriginal, so they are only a weak form of [[incremental backup]] and cannot substitute for a [[full backup]].<ref>{{cite web |last=Chien |first=Tim |title=Snapshots Are NOT Backups |url=http://www.oracle.com/technetwork/documentation/rman-fra-snapshot-322251.html |website=Oracle.com |publisher=Oracle |access-date=4 August 2016 }}</ref> Some systems also use a COW technique to avoid the [[fuzzy backup]]s, otherwise incurred when any file in the set of files being backed up changes during that backup.

When implementing snapshots, there are two techniques: