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Re: [BackupPC-users] OT: udev rule for persistent removable device naming
2012-04-03 17:57:56
On Tue, Apr 3, 2012 at 3:49 PM, Timothy J Massey <tmassey AT obscorp DOT com> wrote:
My backup servers have a SATA removable
drive tray installed in them. Its purpose is to be a target for BackupPC
archvies (among other things) that allows the user to easily swap these.
It is simply a physical tray: the system sees the drive inside
of the tray exactly the same as any other internal SATA drive.
And that's part of my problem. With
RHEL 6, I no longer have consistent (actually, persisitent) device naming.
This system also uses a USB flash drive as its boot drive. It
seems that there is a race condition during bootup. *Most* of the
time, the USB device appears after the SATA drives, but not always. So,
most times my tray shows up as /dev/sdd, but sometimes it shows up as /dev/sde.
As you can imagine, this causes no end of problems with trying to
create a script to safely partition and format the drive!
The (AFAIK) proper way to correct this
is to create a udev rule to assign the tray device a persistent device
name. However, because it's a removable tray, I can't use something
like drive UUID or serial number to do this: the drive changes. I
can't use SCSI path: it's the race condition that causes this one
to change. And because sometimes the drive that I insert will be
perfectly blank (a new drive), I can't use something like a drive label:
it might not have one!
The only thing I *think* I can use is
PCI bus address, and I don't know how reliable that might be. I don't
want some *other* race condition to break things.
Does anyone else have any experience
in this regard and might either be able to either point me in a better
direction or give me an example of a udev rule that uses PCI address? I've
Googled, but everything I can find uses things like drive ID or label.
I can't find a single example with PCI bus address (DEVPATH).
Personally, I'd never trust a script to automatically format a disk just because it is inserted in a certain carrier. Maybe something like making a small permanent partition with a label or UUID would let you detect it and figure out the base device if you really have to format different/larger partition on it in a script. The PCI bus address shouldn't change unless you move controller cards around, though.
--
Les Mikesell
lesmikesell AT gmail DOT com
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