Re: [PATCH] Add VPD support to aacraid

[Hannes Reinecke <hare@suse.de>]

Salyzyn, Mark wrote:
> Hannes, I am working the firmware and management software folks to find out how
> to mine for this information. In your patch, the controller serial
number may be
> helpful, but not necessarily compliant?
>
Well, the information in page 0x80 is 'vendor specific'. So anything we
put in there is compliant :-)

> Besides persistent device id, what else is gained? The controller ensures persistent
> device id for the arrays through the meta-data, only migrating if it
happens to be a
> foreign (from another controller) array that collides with a native
array at the same
> ID. Plug the constituent drives into totally different IDs in the SAS
infrastructure,
> the ID remains the same as presented by the controller. Plug those
drives into another
> controller, and if not taken by an existing array, the ID will again
remain the same.
>
Yes, that's what I thought would happen. Main reason for adding page
0x80 support is to get it to work with the current persistent device ID
setup from udev. There we're using the scsi_id program which doesn't
return a serial number if neither page 0x83 nor page 0x80 are supported.
So just hacking them into the driver was the easiest way to get it fixed.

And there is actually a second reason for adding page 0x80 support:
If there were something like a build uuid for the array (either a proper
uuid or maybe even the build date) we would be able to detect an array
re-initialisation. Currently we won't be able to deal with this as the
array will have the same ID, so we would try to mount a drive with a
totally different content.

That was actually what I was aiming for with that patch, but after two
days of hacking I gave up and settled for the easy way out.
I know that at least the array build date is somewhere, as the
management software displays them :-). So it should be relatively easy
to use that as the serial number.

> If this is all of your concerns, adding the baggage to the driver
> will be redundant.
> 
Actually, not quite. In not supporting EVPD page any compliant software
must assume that there is not way of reliably distinguish between two
drives from the same vendor/model.
And, incidentally, it should be possible to hook in two controllers, and
creating two arrays with the same name, right?
So we _don't_ have a reliable way for doing so.
And this is where EVPD page 0x80 support comes in.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux Products GmbH		S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de
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