Bug#614353: multipath-tools-boot: upgrade to squeeze breaks machines with root on iscsi

[Ritesh Raj Sarraf]

Hello,

On 02/22/2011 05:16 PM, Hanspeter Kunz wrote:
>> Persistence is not available for devices everywhere in the kernel.
>>
>> /dev/sd[??]
>> Not persistent. They can change of reboots based on which one gets
>> discovered first
>>
>> /dev/dm-*
>> Not persistent. These are device mapper devices with the same caveat I
>> mentioned above.
>>
>> /dev/disk/by*
>> I don't know the history behind why it was started. But these entries
>> are symlinks to block devices. Now when block devices are locked (like
>> in your case), you can't use any of these entries.
> 
> well, I guess the main idea of having /dev/disk/by-uuid is to have
> persistence ;)
>

Yes, indeed. But that is not to guarantee that the device is not locked.

> I agree, during boot, when first the iscsi- and afterwards the
> multipath-devices become available, these symlinks have to be changed.
> This worked fine in lenny. If this really doesn't work anymore in sueeze
> in principle (which I doubt) then this should at least be mentioned in
> the NEWS such that people using it are informed.
> 
> On the other hand, I still think that having the disk/by-uuid links for
> the multipath devices would be nice, for various reasons. Most
> importantly, because using the uuid *guarantees* that the system boots
> the intended filesystem. Devices can change (e.g. in the case of iSCSI a
> wrong device could be mapped to the machine, because of a configuration
> error or whatever). Using uuid I would instantly realize that (because
> the machine would not find the root fs).
> 
> This worked on lenny and I would really like to have this feature again
> in squeeze.
> 

I have taken up the multipath-tools maintenance very recently. I can't
really comment on what was in Lenny. But I can talk on multipath best
practices.

In multipath, you can disable "user_friendly_names", which will then
give you access to the unique lun serial id based device names. The
user_friendly_names was a [mis]feature IMO.
So in simple, you can get the same guarantee with multipath also.

>> /dev/mapper/* is the recommended way of using any Device Mapper
>> solution. Be it linear, crypt, multipath, snapshot or anything else.
> 
> I do not agree. All my debian systems (laptops with crypt, servers with
> raid/lvm) boot with /dev/disk/by-uuid root devices. As far as I am
> informed, this is also the debian default (when using grub).
> 
by-uuid does not take care of block devices with no file systems.

-- 
Ritesh Raj Sarraf | http://people.debian.org/~rrs
Debian - The Universal Operating System

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 900 bytes
Desc: OpenPGP digital signature
URL: <http://lists.alioth.debian.org/pipermail/pkg-lvm-maintainers/attachments/20110222/dfdbe0f6/attachment.pgp>