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Old 01-27-2011, 07:41 PM
Chuck Munro
 
Default Static assignment of SCSI device names?

Hello list members,

In CentOS-5.5 I'm trying to achieve static assignment of SCSI device
names for a bunch of RAID-60 drives on a Supermicro motherboard. The
"scsi_id" command identifies all drives ok.

The board has one SATA controller and three SAS/SATA controllers ...
standard on-board ICH-10 ATA channels, an on-board LSI SAS/SATA
controller, and two add-on SAS/SATA contoller cards. There are 13
drives in all, spread across the four controllers, all configured for
Linux software RAID.

The problem is in management of the drive names and figuring out which
drive to pull in case of failure. Unfortunately the BIOS scan detects
only the three drives connected to the ICH-10 SATA controller. That's
ok because that's where the RAID-1 boot drives are. However, when the
kernel starts it assigns those drives last, not first.

For this reason I want to use a set of udev rules to assign specific
names to the drives plugged into specific ports (to maintain my sanity
:-) ).

Identifying drives by their ID string (which includes the drive's serial
number) and assigning names in the rules works ok. BUT, what happens
when I have to swap out a failed drive? The serial number (and possibly
model number) changes, and the udev assignment should fail, probably
assigning an unexpected /dev/sd? name. RAID rebuild would choke until I
change the MD device assignment.

Is it possible to assign SCSI drive names by hardware path instead? I
especially want the three RAID1+spare boot drives to always be assigned
sda/sdb/sdc, because that sorts out other issues I'm having in CentOS-5.

In the udev rules file I tried piping the output of "scsi_id -g -i -u -s
/block/..." through "cut" to extract the path, but I get no match string
when I run "udevtest" against that block device. Does the
"PROGRAM==....." clause not recognize the pipe symbol? I tried a little
shellscript to provide the RESULT match string, but udevtest didn't like
that.

Is there a supported way to predictably assign a drive name according to
the hardware port it's plugged into ... it would make swapping drives a
lot easier, since it becomes 'drive-id-string' agnostic. Better yet, is
there any way to tell the kernel the order in which to scan the controllers?

I'm also hoping the problem doesn't radically change when I install
CentOS-6 on this box. I'm using CentOS-5 just to get practice in using
KVM and RAID-60.

Thanks for any advice you can offer.

Chuck

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Old 01-27-2011, 08:09 PM
Les Mikesell
 
Default Static assignment of SCSI device names?

On 1/27/2011 2:41 PM, Chuck Munro wrote:
>
> Identifying drives by their ID string (which includes the drive's serial
> number) and assigning names in the rules works ok. BUT, what happens
> when I have to swap out a failed drive? The serial number (and possibly
> model number) changes, and the udev assignment should fail, probably
> assigning an unexpected /dev/sd? name. RAID rebuild would choke until I
> change the MD device assignment.

If you can figure things out for the initial md device creation,
subsequent assembly uses the uuid to match up the members and doesn't
care if the disks have been moved around either physically or by
detection order. And if you are hot-swapping drives and rebuilding
manually, you should be able to find the just-assigned name with 'dmesg'.

--
Les Mikesell
lesmikesell@gmail.com

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