# Back up of data before performing pt-online-schema-change.

**URL:** <https://forums.percona.com/t/back-up-of-data-before-performing-pt-online-schema-change/2558>\
**Category:** Percona Toolkit\
**Created:** [May 22, 2012, 5:15am UTC](https://forums.percona.com/t/back-up-of-data-before-performing-pt-online-schema-change/2558 "2012-05-22T05:15:26Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sairam](https://avatars.discourse-cdn.com/v4/letter/s/90db22/32.png) [@sairam](https://forums.percona.com/u/sairam)\
**Post date:** [May 22, 2012, 5:15am UTC](https://forums.percona.com/t/back-up-of-data-before-performing-pt-online-schema-change/2558/1 "2012-05-22T05:15:26Z")

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Hi,

According to the percona’s documentation, it is suggested to have recoverable backups before using the tool. Is this required, for online schema change ?

Because for osc, the tool will create a copy of the table being modified and with --nodrop-old-table option this table can act as back up. In such cases, why is the back up step mentioned in the documentation required ?

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**Author:** ![scott.nemes](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/scott.nemes/32/5_2.png) [@scott.nemes](https://forums.percona.com/u/scott.nemes)\
**Post date:** [May 22, 2012, 12:09pm UTC](https://forums.percona.com/t/back-up-of-data-before-performing-pt-online-schema-change/2558/2 "2012-05-22T12:09:06Z")

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If everything worked 100% as expected (and never failed), we would not need backups for anything. Unfortunately, that is not the case.

So while the backup is not required, it is a good idea to backup your database prior to doing anything that could potentially harm it. =)

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**Author:** ![atxdba](https://avatars.discourse-cdn.com/v4/letter/a/c4cdca/32.png) [@atxdba](https://forums.percona.com/u/atxdba)\
**Post date:** [August 27, 2012, 8:07pm UTC](https://forums.percona.com/t/back-up-of-data-before-performing-pt-online-schema-change/2558/3 "2012-08-27T20:07:38Z")

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When the time comes, you’ll know.

Any kind of change inherently involves some amount of risk. There could be some bug in the tool that despite all best efforts and unit tests around it that gets unearthed in your particular setup.

There could be user error where the tool works as designed but you just told it to do the wrong thing.