[DRBD-user] Ahead/Behind problem

lyre 4169e1 at gmail.com
Mon Aug 20 08:16:38 CEST 2012

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

Hi all:

I have a drbd 8.3.13 compiled on centos 6.2(kernel 2.6.32-220.el6.x86_64)

I tried the Ahead/Behind mode by setting "on-congestion pull-ahead".
Thought I don't exactly understand what does the 'congestion-fill'
parameter mean, by changing it's value, I noticed something amazing.

The manual said the optional values is 0 to 10GiBytes; in my case, I
tried 256K, 4M, 8M, 32M, and 256M, and keep writing data on the drbd device:

with value of 32M or 256M, it works as usual (cs:Connected);
with value lesser than / equal to 8M, Connection state changed from
'Connected' to 'Ahead/Behind'. However, after I stop I/O writing, the
value of 'oos' keep increasing for a short while (that's reasonable) and
stopped at certain value. after that moment, the replication seems to be
stopped, the 'oos' never changed again with 'cs:Ahead/Behind' &
'ds:Outdated/UpToDate' , I'm sured that there's no more I/O on that
device. Unless I disconnect & reconnect it, it would do resync again.

So my questions are:
1. what dows 'congestion-fill' exactly mean?
2. is there something wrong with the above situation?

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