Re: Statically nameing a SCSI device

[Greg KH <greg@kroah.com>]

On Sat, Aug 11, 2007 at 04:25:34PM -0500, gerald.hotplug@sysmatrix.net wrote:
> I know this was discussed recently here:
> <http://sourceforge.net/mailarchive/forum.php?thread_nameÓd656c40708012110o29e111b4w707ee03afb0e71f2%40mail.gmail.com&forum_name=linux-hotplug-devel>
> 
> I wasn't on the list at the time so I'm starting a new thread.
> 
> I have a rather unique situation.
> 
> I have a machine with 20 drive bays. 16 SCSI-SCA and 4 SATA. The
> architecture does not know about the SATA controller until the Linux
> kernel takes over so they cannot be used as boot devices. They need to
> stay at the "end of the device tree".
> 
> I would like to give them persistent names of /dev/sdw, /dev/sdx,
> /dev/sdy, and /dev/sdz.
> 
> But, all of the programs that udev uses to get unique identifying
> information about drives to use in naming rules seem to require that you
> know the kernel name first.

That's because the kernel always names the device first, and than passes
that information off to udev.

> Why does nothing in udev seem to allow one to use standard SCSI
> host,channel,device,lun nomenclature to query a device?

You can do that just fine if you want to, just look at the device chain
for the block device, the information is in there.

> The 4 SATA bays will have drives in all of them long before I fill up 16
> SCA bays. But, every time I add and SCA drive to the primary controller
> all of the SATA drives have their kernel name shifted up one letter so I
> can't use the kernel name to query the device for its serial number.
> 
> These drives are for data storage only but they will probably be formatted
> using LVM so I can create one big mount point without having a symlink
> farm growing so I need to keep stable /dev/sd'x' names for LVM to keep
> track of them.
> 
> Anyone have any idea of what I can use to create a uniquely identifying
> rule for each of these drives so that I can assign static /dev/sd'x' NAMES
> to them at boot time even when the kernel name has changed?

Just look at what gets created for you in /dev/disk/  The information
there should help you.

> Or, can anyone point me to documentation of a clear way to do this in
> kernel space. Eg., to have the kernel always assign the same kernel name
> to a device in a certain range (sdw, sdx, sdy, sdz) based on it's SCSI
> loaction ID (4,0,0,0 -- 4,0,1,0 -- etc.)?
> 
> Thanks,
> 
> Gerald
> 
> P.S.
> 
> Wait a sec, I'm re-reading my message before posting and getting an idea
> but I have too little udev experience to implement it.
> 
> Can I write a set of rules in a 20-local.rules file that will run
> 
> scsi_id -g -s /block/sd'x'
> 
> for every value of 'x' looking for
> 
> "SATA     WDC WD2500YS-01     WD-WCANY1955037"
> 
> And then assigning NAME="sdw"

Yes, you can do just that.

good luck,

greg k-h

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