[DRBD-user] how do i know it works?

Tim Tregubov tim at zingweb.com
Sat May 29 22:05:34 CEST 2004

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


On May 29, 2004, at 3:10 PM, Gregory Golin wrote:

> How do i know it works? From what i read, its a nono to mount the lower
> device on the secondary system. I did it anyway, >:D just to see if
> there is anything there. So after sync, yes, there was data. Then i
> copied around 250Mb to nb0 on the primary system and waited - nothing.
> Remounted /dev/sda1 - and its still empty. Thoughts?

If I'm understanding you correctly the problem is that this simply 
won't work.
A non-shared type filesystem won't recognize changes to the underlying 
device. Therefore although it is possible to mount the drbd device on a 
secondary you won't see changes.

As per the FAQ on drbd.org and I quote:
"Q: Can I mount the secondary at least readonly?
A: DRBD would not care, but most likely your filesystem will be 
confused because it will not be aware about changes in the underlying 
device. This in general means that it cannot work, not with ext2, ext3, 
reiserFS, JFS or XFS. If you need not just a mirrored, but a shared 
filesystem, use GFS or OpenGFS for example. But these are much slower.  
This is the reason why DRBD does not allow mounting the secondary. 
Thus, if you want to mount the secondary, set the secondary as the 
primary first. Both devices mounted at the same time does not work."

All you need to do is switch roles and then the secondary will see 
stuff on the device.

cat /proc/drbd is how to watch progress.  you can:
watch -n1 cat /proc/drbd
if you like progress bars to move.  :-)

I'm a newbie here, so if I'm totally wrong just laugh at me.  :-)

Cheers,
Tim




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