On Fri, 2023-07-07 at 14:26 -0500, Ron Flory via users wrote: > On 7/7/2023 12:42 PM, home user wrote: > > When I try to verify a back-up, I use "diff -r". The directory > > trees > > being compared contain about 870 files (mostly binary, like PNG, > > JPG, > > and so on), and take up about 707 megabytes. The trees being > > compared > > are on the hard drive and on a USB-3 stick. When I run the "diff - > > r" > > command, it seems to finish too quickly - it seems like less than a > > half of a second. I saw similar results a few weeks ago comparing > > about 30 gigabyte trees on the hard drive vs. on a USB-3.1 stick; > > the > > results were practically instantaneous. Is diff actually checking > > every bit (or byte), or is it using some "short cut"? > > Was this immediately after your backup/copy completed? You may be > comparing against the in-memory disk caches. > You may (simply) flush the in-memory disk caches to force reads > from > the external disk with (run as root or sudo): > > sync ; echo 3 > /proc/sys/vm/drop_caches > > then try your diff again.
The point and syncing is important, but aside from that this is frankly a terrible way to compare non-text files. Diff is strongly geared to comparing text line by line, which isn't the OP's use case. I'd suggest working with something like 'rsync --dry-run'. poc _______________________________________________ users mailing list -- [email protected] To unsubscribe send an email to [email protected] Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/[email protected] Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
