[DRBD-user] drbd not working with high mtu?

Dan Barker dbarker at visioncomm.net
Sat Feb 1 14:47:24 CET 2014

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

> -----Original Message-----
> From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-
> bounces at lists.linbit.com] On Behalf Of Harka Gyozo SA
> Sent: Saturday, February 01, 2014 1:32 AM
> To: drbd-user at lists.linbit.com
> Subject: [DRBD-user] drbd not working with high mtu?
> Hi!
> Anyone knows about an issue with mtu?
> I tried to increase it to max ( there are two nics with a crossover cable,
> so
> no switch, router etc.. ). I found that max mtu supported by my card's
> driver
> is 7200.
> ssh, ping (also with big packages), nfs works.
> drbd keeps saying:] block drbd1: [drbd1_worker/16675] sock_sendmsg time
> expired, ko = ...
> If I decrease the mtu to 6000, error message stops, and I can see the
> syncing
> in the /proc/drbd (While the mtu is high it's stalled).
> If I increase the mtu to 6200, kernel message returns, communication
> stalled.
> This is a bug? Or maybe I should increase buffer sizes in the config?
> [ version: 8.3.7 (api:88/proto:86-91) ]
> HARKA Győző
> -----------

ssh, ping, nfs all will fragment packets.

Try ping with a 10K size and the don't fragment switch set. Lower the size until it works.

ping -M do -s 6800 -c 1 <host>


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