# Verifying Backend Data

**URL:** <https://forum.duplicati.com/t/verifying-backend-data/348>\
**Category:** Support\
**Created:** [August 31, 2017, 1:32am UTC](https://forum.duplicati.com/t/verifying-backend-data/348 "2017-08-31T01:32:23Z")\
**Posts on this page:** 1\
**Showing post:** 19

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**Author:** ![JonMikelV](https://forum.duplicati.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@JonMikelV](https://forum.duplicati.com/u/JonMikelV)\
**Post date:** [February 5, 2018, 4:00pm UTC](https://forum.duplicati.com/t/verifying-backend-data/348/19 "2018-02-05T16:00:24Z")

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We’re getting a little bit off topic here, but I’d recommend looking at this post:

> [@Help me setup best backup job strategy for years of photo images...?](https://forum.duplicati.com/t/help-me-setup-best-backup-job-strategy-for-years-of-photo-images/1895/2):
>
> It’s no problem to create a single backup job for your complete photo archive. Deduplication doesn’t work across multiple backup tasks. Creating a single backup job will save remote storage space if (parts of) source files are identical. For better performance, you can increase the block size with advanced option --blocksize. If you set the block size to 500KB, the number of blocks will be reduced with 80% (default block size is 100KB). Queries to the local database will be much faster, the si…

And here Kenkendk says in THEORY a block size of up to 2GB should be supported (though there’s no mention on whether or not that’s a good idea). 😉

> [@"Previous volume not finished, call FinishVolume..." error](https://forum.duplicati.com/t/previous-volume-not-finished-call-finishvolume-error/804/7):
>
> Do you mean you have --blocksize=1GB ? Or was it --dblock-size=1GB? (Annoying name clash …) I am not aware of anyone using so large a setting for blocksize but it should work fine, at least up to 2GB (aka int32.MaxValue).

Overall I’d say a jump from a `--blocksize` of 100KB to 100MB should work just fine, but might be a bit drastic. At the default 100KB you’re looking at 10.7 million block-hash rows per 1 TB of source data.

Shifting to a more modest 1MB block size would take that down to just over 1 million block-hash rows. That won’t necessarily return a 10x smaller sqlite file and 10x faster performance, but should show a fair bit if improvement…

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