[DRBD-user] Limit Syncer Speed

[Jasmin J.]

Hi!

 > Either "pull-ahead" doesn't work, or another configuration interferes with
 > this setting,
Finally I found the reason why it didn't work as expected. It was a small 
sentence in this description:
    https://www.drbd.org/en/doc/users-guide-84/s-configure-congestion-policy
  -> A good value for congestion-fill is 90% of the TCP network send buffer, in
     non-DRBD Proxy setups.

My former "congestion-fill 2G" and "sndbuf-size 512k" could never trigger the
"pull-ahead" state, because the configured fill level simply was never reached.

This is now a working configuration:
disk {
                 al-extents 2000;
                 # Full speed for 1GBit link
                 c-plan-ahead 0;
                 resync-rate 110M;
      }

net {
                 max-buffers 8000;
                 max-epoch-size 8000;
                 sndbuf-size 512k;
                 cram-hmac-alg sha1;
                 shared-secret "xxxx";
                 verify-alg md5;
                 protocol A;
                 on-congestion pull-ahead;
                 # should be 90% of the TCP send buffer if no DRBD Proxy is used
                 congestion-fill 460k;
                 # should be 90% of the al-extents
                 congestion-extents 1800;
     }

So again: Good job, Linbit!

Maybe a sample configuration in the documentation for such scenario would be
nice for others.

BR,
    Jasmin