# Checksums during back up?
**URL:** https://forum.duplicati.com/t/checksums-during-back-up/12795
**Category:** Support
**Created:** [July 30, 2021, 7:11am UTC](https://forum.duplicati.com/t/checksums-during-back-up/12795 "2021-07-30T07:11:59Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@sisyphosloughs](https://forum.duplicati.com/u/sisyphosloughs)
#### Post date: [July 30, 2021, 7:11am UTC](https://forum.duplicati.com/t/checksums-during-back-up/12795/1 "2021-07-30T07:11:59Z")
Hi all,
I‘m searching for a cross-platform backup. Due to encryption, Duplicati is a candidate!
I may ask how Duplicati will ensure the integrity of files when backing them up. Are checksums used when reading and writing the files to be backed up?
Regards
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### Author:  [@ts678](https://forum.duplicati.com/u/ts678)
#### Post date: [August 1, 2021, 12:20pm UTC](https://forum.duplicati.com/t/checksums-during-back-up/12795/2 "2021-08-01T12:20:05Z")
Welcome to the forum @sisyphosloughs
> [@sisyphosloughs](#):
>
> I may ask how Duplicati will ensure the integrity of files when backing them up. Are checksums used when reading and writing the files to be backed up?
This is a two part question because the files at the backup destination are very different from the source.
[How the backup process works](https://duplicati.readthedocs.io/en/latest/appendix-a-how-the-backup-process-works/)
Source files have a hash computed at backup time which is verified at restore time at default setting, but
[skip-restore-verification](https://duplicati.readthedocs.io/en/latest/06-advanced-options/#skip-restore-verification) can turn off the verification to go faster, although this seems like a less safe plan.
> `--skip-restore-verification = false`
> After restoring files, the file hash of all restored files are checked to verify that the restore was successful.
> Use this option to disable the check and avoid waiting for the verification.
Files for the destination have a hash computed at creation time prior to upload. Verifying the hash after an upload isn’t done by default because it might require a download of the file just uploaded. Instead, a listing of files is done after backup to see if what’s expected is seen at expected size. A sample test is done too:
[Verifying backend files](https://duplicati.readthedocs.io/en/latest/03-using-the-graphical-user-interface/#verifying-backend-files)
To do heavier sampling of destination files, one can use [backup-test-samples](https://duplicati.readthedocs.io/en/latest/06-advanced-options/#backup-test-samples) or [backup-test-percentage](https://duplicati.readthedocs.io/en/latest/06-advanced-options/#backup-test-percentage).
[The TEST command](https://duplicati.readthedocs.io/en/latest/04-using-duplicati-from-the-command-line/#the-test-command) explains what a sample is (usually 3 files, but a given file is not done twice in a run).
Regardless of checksums, it’s good practice to test restore occasionally, including [disaster recovery](https://duplicati.readthedocs.io/en/latest/03-using-the-graphical-user-interface/#restoring-files-if-your-duplicati-installation-is-lost) use.
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### Author:  [@sisyphosloughs](https://forum.duplicati.com/u/sisyphosloughs)
#### Post date: [August 1, 2021, 4:22pm UTC](https://forum.duplicati.com/t/checksums-during-back-up/12795/3 "2021-08-01T16:22:43Z")
@ts678 thanks for the detailed explanation!