[Bug 9407] New: rsync transfers cause zero window packets

samba-bugs at samba.org samba-bugs at samba.org
Fri Nov 16 18:24:37 MST 2012


           Summary: rsync transfers cause zero window packets
           Product: rsync
           Version: 3.0.9
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P5
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: emmett at webengineer.com
         QAContact: rsync-qa at samba.org

I am using BackupPC with rsync daemons running on the target machines.  Some
targets are virtual and some are on their own hardware.

A couple of months ago I noticed that one of the VM targets always failed to
get a backup, and upon investigation I found that the packet stream contained
lots of zero window and keep alive packets.

The failure turned out to be caused by a wrong VM network driver on that
particular VM and after resolving that all backups completed.  However that
caused me to look into it further when I discovered that fixing the driver did
not stop the zero window packets from happening and upon further investigation
I discovered that ALL backup sessions are seeing lots of zero window packets,
then further investigation shows that backups are taking way too long; as long
as ten hours for a 35GB backup.

I've googled for zero window errors with rsync and nothing I've found points to
anything that could resolve my issue.  But how can that be?  Am I the only one
seeing this issue?  Or is it that no one is looking?

I am running CentOS 6 and Fedora 17, all of which have rsync 3.0.9-1, except
one, which has 3.0.6-9.  I have a Gigibit LAN and iperf shows that there is a
solid 900+Mbs throughput in both directions to/from all target machines and the
backup server.

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