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[Discuss] Disk numbering



On Sat, 2011-10-01 at 14:36 -0400, Jerry Feldman wrote:
> On 10/01/2011 10:49 AM, Matt Iavarone wrote:
> > On 10/01/2011 10:26 AM, Jerry Feldman wrote:
> >> 2 weeks ago when I added a new 1.5TB ($49) HD to use as backup, my
> >> drives were numbered sda, sdd, sde, and sdf. This prompted me to rewrite
> >> my weekly disk health script to discover what drives are on my system.
> >> All well and good. My /etc/fstab uses only UUID as does my RAID1. I shut
> >> my system down last week when I went out of town for a couple of days,
> >> and I found that the drives were renumbered again. I don't recall the
> >> exact numbering, since I don't have anything that uses the drive numbers
> >> other than my health script.  When I returned, I noticed an I/O error on
> >> the new drive so I spent hours running fsck to bypass the bad blocks and
> >> fix any errors. I'm watching closely to see over the next few days in
> >> case I need to return the drive. After the fsck was completed, and the
> >> drive tested good, I rebooted, and this morning I noticed another
> >> renumbering (sda, sdb, sdc, sdd). The backup drive that was repaired is
> >> still /dev/sdc. Now sda and sdb are the RAID1 pair.
> >>
> >> I guess I am just ranting because I know the kernel assigns the drive
> >> numbers at boot time and I don't need to know anything about the drive
> >> numbers unless I need to run something manually.

There is an extension to SCSI called the SCSI Enclosure Services (SES)
that can report disk ordering, and I have proposed additions to ACPI for
manufacturers to provide such ordering in their DSDTs, but fundamentally
the problem is that the Linux community doesn't care enough about
solving this problem in the way that users like yourself are asking. 

There is a belief that udev rules and so on will solve everything but
the kernel and tools still deals with block device names in many places.
Until we get beyond the desktop-centric view that no admin needs to know
what kernel device names are in use, this is an ongoing problem.

> > If you have dependencies on the disk lettering, then you can use udev
> > rules to force them.

> True, but the best way is not to depend on disk numbering at all,
> especially when you have removable drives like I do. In my case above it
> was just a bit comical that they got renumbered several times in the
> last couple of weeks.

This kind of thing drives me nuts too. I'm trying to get this stuff
fixed properly when I have cycles by requiring that system vendors
provide information about slot arrangements and we solve this the right
way - changing enumeration, use of volume UUIDs, etc. are all hacks.

Jon.





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