Re: disk/by-label + label-change

["T. Horsnell" <tsh@mrc-lmb.cam.ac.uk>]

Sorry - forgot to CC: the list.

>On Tue, 2006-12-12 at 17:51 +0000, T. Horsnell wrote:
>> >On 12/12/06, T. Horsnell <tsh@mrc-lmb.cam.ac.uk> wrote:
>> >> If a disk with a persistence-entry in /dev/disk/by-label
>> >> is re-labelled with tune2fs, the by-label entry isnt
>> >> updated to match the new label and when the disk is mounted
>> >> with a 'mount -L ',
>> >
>> >You are writing to a raw sector of the disk, no part of the system
>> >will notice that you did this and have changed something. You need to
>> >tell the kernel to emit an event by doing:
>> >  echo "add" > /sys/block/sda/uevent
>> >and the link will get updated.
>> 
>> OK, thanks. But shouldnt tune2fs do this when it updates the label?
>> I guess I should make my own tune2fs script and do it there.
>
>Right, that shouldn't be part of the tool that writes to the disk, it
>can't know if it's safe to update the links.
>
>> >> the mounted-device shows up as something
>> >> like:
>> >>
>> >> [root@dev1 ~]# mount
>> >> /dev/hdb2 on / type ext3 (rw)
>> >> proc on /proc type proc (rw)
>> >> sysfs on /sys type sysfs (rw)
>> >> devpts on /dev/pts type devpts (rw,gid=5,modeb0)
>> >> tmpfs on /dev/shm type tmpfs (rw)
>> >> none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
>> >> sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
>> >> >>>> /dev/.tmp-8-17 on /test type ext3 (rw)
>> >>
>> >> Is this as it should be?
>> >
>> >Looks like you mounted the device with a PROGRAM rule, right? This is
>> >definitely not what it "should be". :)
>> 
>> I do no mounting in udev, its all in fstab. I never thought to
>> do it in a udev PROGRAM rule...
>
>But who is using udev's temporary device node for mount then?
>  /dev/.tmp-8-17 on /test type ext3 (rw)
>
>That usually only exists during the udev event processing.

Hmm. Of course, I cant reproduce this.
But would you mind a related question? The reason I'm doing
all this stuff is because of an NFS problem associated
with moving disks around on the SCSI bus.

I have a fileserver which NFS-exports a bunch of filesystems
to a compute farm. The compute farm clients mount these with
the 'hard' option so that they stall if they try and make NFS
requests while the server is offline.
From time-to-time I make changes in the SCSI configuration
of the server (like moving a SCSI shelf to a different SCSI
adapter).
Without udev persistence rules, the /dev/sdN device for
the SCSI disks may change as a result of the shuffle, and
my farm clients then sometimes mistakenly access the filesystem
on the *old* /dev/sdN. There are no NFS errors, just wrong
filesystem contents. I cant use the /dev/disk/by-whatever
symlinks because they resolve to the changing /dev/sdN

So I make persistence rules such that my disks *always* mount
on the same /dev/dskN regardless of where they are on the bus,
but then NFS complains of a 'stale filehandle' if server filesystems
are moved around. This is a bit better than continuing with the wrong
data, but it would be best if NFS knew that the disk was the same 
disk, even tho it was on a different SCSi bus/slot in the server.

Should this be possible with persistent device names?

Thanks,
Terry

>
>Kay
>
>

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