Re: [PATCH] path_id: Handle SAS and SATA devices

[Hannes Reinecke <hare@suse.de>]

David Zeuthen wrote:
> Hi,
> 
> On Mon, Jul 12, 2010 at 10:47 AM, David Zeuthen <davidz@redhat.com> wrote:
>> On Mon, 2010-07-12 at 11:07 +0200, Kay Sievers wrote:
>>> On Wed, Jul 7, 2010 at 16:55, Hannes Reinecke <hare@suse.de> wrote:
>>>> SAS devices should be referenced by the SAS address of the target;
>>>> on the initiator side we assume an identity mapping between SAS
>>>> addresses and PCI devnumber.
>>>> SATA devices have an identity mapping between SATA links and
>>>> linux scsi_host structures, so we can map the host number onto
>>>> the SATA link.
>>>> For this to work the LUN numbering needs to be updated, too,
>>>> as SATA devices do not have the concept of a LUN, whereas normal
>>>> SCSI devices have.
>>> David, any chance to give this a try on your SAS box, and see if this
>>> works as expected for you too?
>> Sure, will do later this week - it's currently powered off and in a
>> moving box!
> 
> OK, I get these additional links in /dev/disk/by-path
> 
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f362-lun-0x0000000000000000
> -> ../../sds
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f363-lun-0x0000000000000000
> -> ../../sdr
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f442-lun-0x0000000000000000
> -> ../../sdq
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f443-lun-0x0000000000000000
> -> ../../sdp
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f522-lun-0x0000000000000000
> -> ../../sdo
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b83f523-lun-0x0000000000000000
> -> ../../sdn
> +│   ├── pci-0000:06:00.0-sas-0x500000e01b843d92-lun-0x0000000000000000
> -> ../../sdm
> +│   └── pci-0000:06:00.0-sas-0x500000e01b843d93-lun-0x0000000000000000
> -> ../../sdl
> 
> for four SAS disks with two paths each. Btw, the WWN used is
> apparently not that of the actual disk
> 
>  # udevadm info -q all -n /dev/sdn|grep ID_WWN>  E: ID_WWN=0x500000e01b83f520
> 
> which matches what is printed on the actual disk
> 
>  http://people.freedesktop.org/~david/FUJITSU-MAY2036RC-sas-disk-picture.jpg
> 
> however the WWNs that your patch introduces differ from this. However
> those WWNs appear here
> 
>  # smp_discover /dev/bsg/expander-7\:0 --multiple |grep b83f52
>  phy   4:T:attached:[500000e01b83f523:01  t(SSP)]  3 Gbps
>  # smp_discover /dev/bsg/expander-7\:1 --multiple |grep b83f52
>  phy   4:T:attached:[500000e01b83f522:00  t(SSP)]  3 Gbps
> 
> e.g. the WWNs that you use are the WWNs of the actual ports, not the
> LUN itself, yes? You should probably use the LUN WWN instead. I mean,
> I think people are interested in the WWN of the LUN and they don't
> care so much about the WWN of the ports. Or maybe we want both?
> Anyway, I *think* that's the way it works but I could be wrong on some
> of the SAS details.
> 
No, that was _exactly_ my intention.
'by-path' is the physical path, ie the path is identified by the physical
properties. Hence we need to refer to the SAS port WWN here.
The WWN of the disk is referred to in 'by-id'.

So the path_id program is working as expected from my POV.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
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