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

Dave Taht dave.taht at gmail.com
Sat Nov 17 01:39:40 MST 2012

On Sat, Nov 17, 2012 at 2:24 AM,  <samba-bugs at samba.org> wrote:
> https://bugzilla.samba.org/show_bug.cgi?id=9407
>            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?

There have been so many interesting bugs fixed in the last year in the
network stack, that I have no idea where to start.

> 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.

This strikes me as the wrong list for this problem.  I would argue in
favor of putting a packet capture up, and telling people on
linux-netdev about it.

Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html

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