[DRBD-user] DRBD (0.6) slows down the application

Lars Ellenberg Lars.Ellenberg at linbit.com
Thu Aug 18 10:40:18 CEST 2005

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

/ 2005-08-17 22:10:28 +0200
\ Hans Holm:
> First time connecting and after a successful "Full Sync" everything is
> OK and all reponse times are normal!
> BUT after a disconnection and a new connect, drbd makes correctly a
> "QuickSync", the response times when Connected now follows the "-t 20"
> parameter value above. 
> Changing this parameter I can change the respone time accordingly.
> The slower machine is always Primary when the problem occurs.
> With the help of tcpdump and some trace printouts inside drbd my
> understanding of drbd behavior look like this:
> Connection phase looks Ok, same as after "FullSync".
> Then after each data transfer from Primary to Secondary, the Secondary
> acknowledged at TCP level Ok but the "DRBD Data Acknowledge" is
> missing.
> After "-t 20" (2 seconds) Primary got response timeout and sends a
> DRBD_Ping, to try the connection, which Secondary immediately
> acknowledged and immediately after this the Secondary also sends the
> missing "DRBD Data Acknowledge". 
> When Primary receives "DRBD Data Acknowledge" it sends next Data
> block, waits for response 2 seconds, times out and sends DRBD_Ping
> "und so weiter"..........  Result is a 2 seconds delay for every disk
> access..
> Have anyone seen this situation and perhaps even know how to solve it.
> I would be very grateful for any kind of help and information.

since you seem well able to use printk and tcpdump, please have a look
whether the "WriteHint" packets are actually sent and received.
if not, I probably know a solution (patchlet).

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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