[Request] dsync --write-verify option?

Hi,

We are looking at ways to increase the performance of dsync -c (content) compare. As you would imagine, this can be very time-consuming but at the same time users want this "to be sure" that final sync has an exact copy of their data.

We can do a lot of syncs before final-sync and cut-over to a new file system. However, the dsync -c right now is all or nothing and that takes a long time then for a final-sync for cut-over and that final-sync is when users are "down" so they don't make any changes.

If dsync had an option somewhere between -c (content) and -lite (like dcmp), then it could be ideal when for when doing a series of dsync before final-sync.

This the -lite-content option compares size, mtime and atime (assuming --open-noatime is used as well) such that if all 3 match then content is not compared. But if one is different (even if just atime) the full content is compared.

Thank you for these great utilities!

• Mark

Start by reading the dsync implementations for -c, -lite, and the related dcmp comparison behavior. Define the new option's semantics around size, mtime, and atime, including --open-noatime, and confirm that content is compared only when those attributes differ; done means the behavior is covered by appropriate tests.