O_DIRECT, avoiding system cache?

Tomasz Chmielewski mangoo at wpkg.org
Sat Mar 13 05:35:28 MST 2010

Is it possible (planned?) to make rsync avoid going through system cache 
and use direct IO?

Right now, if you decide to backup your desktop system (but it's not 
only about desktop systems; rather more about one-time-only data 
transfers) to external disk, you will notice that your X session lags 
terribly, mainly because:

- system caches everything what rsync reads from the original drive,
- system caches everything what rsync writes to the destination drive,
- while doing the above, current cache is being empties.

I've seen some discussions on rsync mailing list in the past about such 
a feature (avoiding using system cache), but I'm not sure if there were 
any conclusions out of it.

Tomasz Chmielewski

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