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Re: SCSI Device Addresses


On Sat, 2008-03-01 at 14:31 +1100, Hamish Moffatt wrote:
> On Fri, Feb 29, 2008 at 12:01:49PM -0500, Lennart Sorensen wrote:
> > UUIDs work for me.  Driver modules load in parallel and nothing will
> > ensure consistent device names.  A unique identifier for the filesystem

No it doesn't, hence this thread.

The hardware RAID card I am working with only presents a SCSI "device"
to the OS if
disk array is present.  Remove the array and the SCSI "device"

> Doesn't udev assign constant sdN/hdN identifiers? It appears to look up
> the drive serial number and attempt to do this.

From what I've observed hdN is consistant.  hda is *always*
hdd is secondary-slave, and so forth.

But for SCSI the mapping is done on a controller/device/lun mapping and
sda is assigned to the lowest c/d/l device.  As my hardware raid cards
are not present devices for disk arrays not present sda is not fixed to
any particular hardware.  In fact and install time when no disk arrays
where configured the SATA disk was assigned to sda.  When I configured
one disk array it then became sda and the SATA disk sdb and the system
didn't boot.  Pull the disk array and the SATA returns to sda.

> Also, if you run LVM or software RAID then you get static identifiers
> out of those automatically, even with the underlying disks moving
> around.

Yes, but you need fixed physical device addresses to create the LVM or
software RAID devices in the first place.

Steve Dobson

It takes two to tell the truth: one to speak and one to hear.

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