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==In computer storage==
COW is used as the underlying mechanism in file systems like [[ZFS]], [[Btrfs]], [[ReFS]], and [[Bcachefs]],<ref>{{cite web |last=Kasampalis |first=Sakis |date=2010 |title=Copy-on-Write Based File Systems Performance Analysis and Implementation |page=19 |url=https://sakisk.me/files/copy-on-write-based-file-systems.pdf |access-date=10 November 2023 |archive-date=5 May 2024 |archive-url=https://web.archive.org/web/20240505220510/https://sakisk.me/files/copy-on-write-based-file-systems.pdf |url-status=live }}</ref> [[ReFS]], and [[Bcachefs]], as well as in [[logical volume management]] and database servers such as [[Microsoft SQL Server#Replication Services|Microsoft SQL Server]].
In traditional file systems, filemodifying changesa file overwriteoverwrites the original data blocks in place. WithIn a copy-on-write (COW) file system, whenthe changesoriginal areblocks made,remain aunchanged. newWhen versionpart of thea file is createdmodified, whileonly keepingthe affected blocks are written to new locations, and metadata is updated to point to them, preserving the original intactversion until it’s no longer needed. This approach enables features like [[Snapshot (computer storage)|snapshots]], which capture the state of a file at a specific time without consuming much additional space. Snapshots typically store only the modified data and are kept close to the original. However, they are considered a weak form of [[incremental backup]] and cannot replace a full backup.<ref>{{cite web |last=Chien |first=Tim |title=Snapshots Are NOT Backups |url=https://www.oracle.com/database/technologies/rman-fra-snapshot.html |website=Oracle.com |publisher=Oracle |access-date=10 November 2023 |archive-date=10 November 2023 |archive-url=https://web.archive.org/web/20231110024434/https://www.oracle.com/database/technologies/rman-fra-snapshot.html |url-status=live }}</ref>
