Can GEOM be used to intercept the I/o calls to an existing mounted device?

[Mark Gladman]

On Thursday 10 July 2008 22:41:25 Tapan Chaudhari wrote:
> Hi All,
>     I am a newbie to FreeBSD and GEOM. I wanted to intercept the i/o calls
> going to a particular mounted device by writing some driver.
> I came across  geom and thought it might work. I tried to create a new
> device, mount it and then tried using gmirror to mirror the device :-
>
> #dd if=/dev/zero of=file1 bs=1M count=10
> #dd if=/dev/zero of=file2 bs=1M count=10
> #mdconfig -f file1
> #mdconfig -f file2
> #fdisk -B /dev/mirror/md0
> #newfs /dev/mirror/md0s1
> #mkdir /mnt/mirror0
> #mount /dev/mirror/md0s1 /mnt/mirror0/
>
> #gmirror label -v -n -b round-robin gm0 /dev/md0
> gmirror: Can't store metadata on /dev/md0: Operation not permitted.
>
> It gave me this error "gmirror: Can't store metadata on /dev/md0: Operation
> not permitted."
>
> Am I doing something wrong? Or GEOM does not permit me intercept the i/o
> calls? If not geom, is there any other mechanism by which I can achieve it?
>
>
> Thanks,
> --Tapan.
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Hey,

You're attempting to set up gmirror on a mounted device. 
Unmount /dev/mirror/md0s1 then retry the gmirror command and it should work.

Cheers!
Mark