[DRBD-user] syncing to disk

Scott Beck sbeck at gossamer-threads.com
Tue Mar 1 02:04:49 CET 2005

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


I ran into a problem last week when one of our servers went down hard. A
lot of information was lost (had to restore from backup). What I think
is happening is data is not being synced to disk in a timely manner. I
can replicate this with just one server using drbd. Here are my steps to

a. make partition primary, so /proc/drbd is in state Primary/Unknown
b. mount partition
c. copy linux src tree to partition
d. hard reboot.

The write cache on the ide disks are meant to flush every 5 seconds. The
write cache in linux is meant to flush every 30 seconds by default I
believe or if the cache is 40% full.

I have tried waiting at least 30 seconds and still saw the error. I
haven't tried doing an actual `sync` command, so I'm not sure if it's
the linux buffer, or the ide buffer. I suspect linux, as I did try the
same test on a reiserfs partition and didn't lose any files.

I am continuing to research this, if anyone has a suggestions please let
me know.


-------------------- Gossamer Threads Inc. ----------------------
Scott Beck                      Email: scott at gossamer-threads.com
Lead Software Developer         Phone: (604) 687-5804
http://www.gossamer-threads.com Fax:   (604) 687-5806

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