[dm-devel] [PATCH] multipath: change default configuration parameters

[Hannes Reinecke]

On 01/16/2013 10:24 PM, Christophe Varoqui wrote:
> On mar., 2013-01-15 at 23:14 +0100, Xose Vazquez Perez wrote:
> ...
>> scsi_id is going to be replaced in systemd(recently udev was
>> included in systemd).
>>
>> See sg_inq(--export option) from sg3_utils.
>
> We will need to patch sg_inq to report a denser id than the documented
> SCSI_IDENT_<assoc>_<type>=<ident>
>
Why? It took me ages to implement that one properly.
And it's only strings, which can be expanded at will.
Plus I have a set of udev rules mangling those into the usual ID_XXX 
variables.

I don't see why we need to change that ...

> Time to launch a debate over the pertinence to maintain the '3' prefix
> scsi_id insisted on prepending to the wwids ... Lennart will take the
> blame without flinching I'm sure ;)
>
It's not '3'.

The '3' is the VPD designator ID as defined in the spec. And it's 
attached there so that you can differentiate between several IDs, 
which might be identical otherwise.

The original idea behind the prefix was that each ID has a different 
level of 'uniqueness'.
Basically, there are 5 possible designator IDs for the LUN:

0: Vendor specific
1: T10 Vendor ID based
2: EUI-64 based
3: NAA
8: SCSI Name string

of which 0, 1, and 8 are basically arbitrary. We only have a 
guaranteed unique ID when the designator is of type 2 or 3.
So prefixing the designator number allows you to figure out whether 
it's a good idea for using that ID.

Mind you, that was when all was encoded in scsi_id.
Now that's all open-coded with udev rules you have different 
variables for each ID, so it's easy to figure out.

But sorry, we can't change that.
Upgrade will be _HELL_ if you do that.

Btw, a patch to the udev rules is attached. It's not yet included in 
the upstream sources as Kay and I are still discussing whether we 
should split the original rule set.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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