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I have been using Unison in a star topology to synchronize my two machines through a server. Now I'm trying to replace the server with storage on rsync.net. However, synchronization requires checking the access times in both replicas, which takes rather long on the remote (10-20 minutes) compared to the local replica (less than a minute).

The remote node is "passive", i.e. can only change through synchronization with other nodes. Seems that the scanning of access times on a passive node could be avoided to speed things up.

Is there a way to use such a constraint in Unison? Or possibly other synchronization software?

pkarnakov
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  • I am also a (happy) rsync.net customer using `unison`. Sometimes the load on their machines is so high that the file system scanning is slow. I do not usually experience delays that large, but sometimes it takes time, indeed. Is the problem persistent? – Edward Mar 15 '21 at 14:29
  • Just tried again a fresh `unison` scan with new replicas (30GB, 150K files). Local was done in under 30 seconds, remote took an hour. – pkarnakov Mar 15 '21 at 16:24
  • Actually it seems better now. Yesterday, any subsequent update took at least ten minutes, now seems quicker (less than a minute). Alright, I will use the current config for now, and keep simple `rsync` in case `unison` takes too long. – pkarnakov Mar 15 '21 at 16:44
  • If the problem persists, get in touch with them. I've had a similar experience a while ago, lasting too long for me, and they moved me to another server. But first I did everything on my side that I thought useful for them as well as for me : reducing the number of files, removing redundant stuff, ... I presume they experience heavy memory pressure, so likely your directory tree is not in cache. Do you have large timeouts when you repeat a scan quickly after a successful one? – Edward Mar 16 '21 at 07:37
  • A scan repeated after a successful one only takes a couple of seconds. – pkarnakov Mar 16 '21 at 08:22
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    In that case, anything you can do to make the number of directory entries to scan smaller, should decrease your timeouts. That means reducing the number of files (if you can). And by the way, I forgot to give you this link (see item in the FAQ about improving performance): https://alliance.seas.upenn.edu/~bcpierce/wiki/index.php?n=Main.UnisonFAQTips – Edward Mar 16 '21 at 08:34

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