Date: Sun, 24 Feb 2013 15:32:10 -0800 From: "Ronald F. Guilmette" <rfg@tristatelogic.com> To: freebsd-fs@freebsd.org Subject: Hard drive device names... Serial Numbers? Message-ID: <2511.1361748730@server1.tristatelogic.com>
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Today I am diddling with a system of mine that already... before today...
contained three SATA drives. I just now added to this system one old
PATA drive I had lying around which I plan to use as a swap drive.
The motherboard for the system in question has two of the older PATA
ports (supporting up to four devices) and then also four SATA ports.
It appears that the BIOS numbers the PATA devices first, and that FreeBSD
just follows suit. Thus, for FreeBSD, whatever drive is the (PATA)
primary master gets the name ada0, the primary slave, ada1, the secondary
master ada2, the secondary slave ada3, and then the SATA ports get names
ada4, ada5, etc.
So anyway, adding the PATA drive to this system of course rendered
everything I had previously had in my /etc/fstab suddenly incorrect.
Fortunately, I anticipated this and was prepared to boot FreeBSD Live
from a CD, and then go in and edit my /etc/fstab as necessary to
adjust everything for the new hard drive numbers.
This isn't the first time I've had to go through this process. It is
always an annoyance.
Up until today I was only dimly aware of the different approach described
here:
http://www.freebsd.org/doc/handbook/geom-glabel.html
but today I was finally motivated to seek out and read the above page,
which I have now done.
Having now read all about temporary labels, permanment labels, and ufsids,
and having noted the obvious drawbacks to each (including but not limited
to the fact that these techniques generally only appear to be applicable
exclusively to UFS file systems _and_ only recently created ones at that)
I thought that I would take a second and ask about the general idea of
using built-in hard drive serial numbers as a filesystem-independent
and interface-independent way of identifying specific hard drive devices
(and/or their sub-parts) e.g. within /etc/fstab.
This idea seems so obviously that I am forced to assume that I'm probably
far from the first person to have suggested and/or asked about it.
So what gives? Why can't we have something like /dev/hdsn/ (hdsn ==
Hard Drive Serial Number) where a set of device numbers would automagically
be created within that directory, all of whose names correspond to the
actual hardware serial numbers of all currently attached hard drive
type devices? (If just the serial numbers are not seen an being unique
enough, I can imagine other unique or semi-unique properties of the drive
being concatenated with the serial numbers.)
It is easy also to envision obvious extensions to such a scheme. For
example, a node named /dev/hdsn/1mgbhxed.s1a might represent the BSD
"a" partition of MBR slice number 1 within the drive whose serial
number is "1mgbhxed".
Anyway, the whole point here is to have a naming convention that would
work across both UFS and non-UFS filesystems, and also/even across both
recently created UFS file systems which include the recently introduced
ufsids as well as older pree-existing UFS filesystems.
So, um, has any idea along these lines been disucssed previously? If so,
what were the arguments for and against?
Regards,
rfg
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