[Bug 9783] New: please don't use client-server model for local copies

samba-bugs at samba.org samba-bugs at samba.org
Wed Apr 10 13:22:54 MDT 2013


           Summary: please don't use client-server model for local copies
           Product: rsync
           Version: 3.0.9
          Platform: All
               URL: http://lwn.net/Articles/400489/
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: mh+samba-bugzilla at zugschlus.de
         QAContact: rsync-qa at samba.org


rsync is quite slow when compared to cp while copying from a local disk to
another local disk. rsync is not made for that situation, but still a common
use case. On linux, this setup misleads CPU frequency governors which causes
CPUs to reduce their operation frequency, resulting in bad performance. On my
test system, rsync copies from disk to disk with about 30 Mbytes/s, while a
simple cp delivers 130 Mbytes/s.

There are shell scripts around that use rsync --dry-run to find out the list of
files that need to be copy and then feed that file list to cp to get better
performance, which is a really really ugly hack.

Please consider detecting a local operation and not using the client-server
model here, but instead using a more stupid algorithm like the one that cp
uses. That would make rsync incredibly more useful in the quite common case of
local operation.


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