[DRBD-user] drbd 0.8 active/active and lvm - What stupid thing am I doing?

Lars Ellenberg Lars.Ellenberg at linbit.com
Thu Jan 18 14:39:20 CET 2007

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


/ 2007-01-18 12:22:06 +0000
\ Graham Wood:
> 
> >lvm.conf:
> >filter = [ "r|/dev/<real blockdevice>|" ]
> Because I only use LVM for the cluster, I've actually got a filter such that lvm only uses /dev/drbd

hm. ok. so you are probably _not_ bypassing drbd.
you may still have a cache coherency problem, though,
see below.

> My mail to the list got stuck (due to me typoing) and last night I rebuilt the platform based on rc2.
> 
> I'm going to try and recreate the problem tonight, and will post back.

when you read the device to calculate that md5sum,
try something which does direct io.
or try "blockdev --flushbufs /dev/ice"  beforehand.
if you have a recent kernel,
try "echo 3 > /proc/sys/vm/drop_caches".

clvm does only make sure you won't messup the lvm meta data.
it does not take care of cache coherency for the page cache of those
block devices.

on the receiving side, drbd does modify the content of the block device
directly -- I'll take patches to notify the page cache about that, to
make it drop the corresponding pages :->

-- 
: Lars Ellenberg                            Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :
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