[DRBD-user] repeatable, infrequent, loss of data with DRBD

Matthew Vernon mcv21 at cam.ac.uk
Thu Sep 3 17:55:51 CEST 2015

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


Hi,

On 22/08/15 10:07, Lars Ellenberg wrote:

Sorry for the delay - it took a while to sort out the necessary
debugging output &c.

> You should also collect /proc/drbd, and maybe dmesg -c,
> before and after each step.
> 
> Especially for the "failed" runs, /proc/drbd and
> the kernel log of both nodes would be relevant.

I have done this, and also collected network dumps (for ports 7790, the
drbd-resource port and 22, the ssh port).

The attached tarball contains the following files relating to 2
iterations of my script (1 failure, the other success):

script-output.txt - output from the script at the "driving" end -
includes /proc/drbd dmesg -c and so on

syslog-16-16-04.txt - syslog from the "target" end for the successful run

15-09-03-16-16-04.pcap - packet dump (tcpdump -w) for the successful run

syslog-16-16-06.txt & 15-09-03-16-16-06.pcap - syslog & packet dump from
the failing run

each iteration through the loop (this is 2 iterations) does, roughly:

* output timestamp
* start tcpdump
* debug
* drbd - create-md and up on both machines, wait-connect,
new-current-uuid --clear-bitmap, primary
* debug
* set magic string (TESTDATAMAGIC)
* debug
* secondary, make remote primary
* debug
* check for magic string on remote (and output FAILED if fails)
* debug
* drbdadm down (both machines)
* debug
* dd 1M of zero to front of underlying LV (both machines)
* debug
* kill tcpdump
* output "Iteration done"

where debug = output the top 5 lines of /proc/drbd,  and dmesg -c

I hope that's enough debugging for you to track down the bug :-)

Regards,

Matthew
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