Re: power interruption -> renamed USB disk

[Ron Johnson <ron.l.johnson@cox.net>]

On 03/07/2011 11:25 PM, Ross Boylan wrote:
> On Mon, 2011-03-07 at 18:02 -0600, Ron Johnson wrote:
> > On 03/07/2011 03:08 PM, Ross Boylan wrote:
> > > I have a SATA disk in an external USB docking station.  The computer it
> > > is attached to is on UPS, but the external disk has only surge
> > > protection.
> > >
> > > When the power goes out for a moment, the disk, which was /dev/sdc,
> > > seems to come back as /dev/sdd.  The disk has a partition that is part
> > > of an LVM volume group, and the file system on the disk is inaccessible.
> > >
> > > I've had to restart the system to get the disk back.
> > >
> > > Is there a better way (aside from getting  the disk on UPS)?
> > >
> > > Debian Lenny (mostly), 2.6.26-2-686 stock Debian kernel on Pentium 4
> > > chip w/hyperthreading.  The disk uses the GPT partition format.
> > >
> > > Most recent incident:
> > > <log>
> > > #power fails
> > > Mar  7 11:21:18 corn kernel: [182529.931888] ethfast: Link is Down
> > > Mar  7 11:21:18 corn kernel: [182530.140155] usb 5-3: USB disconnect, address 4
> > > Mar  7 11:21:18 corn kernel: [182530.140155] usb 5-3.1: USB disconnect, address 7
> > > Mar  7 11:21:18 corn kernel: [182530.140155] usb 5-3.2: USB disconnect, address 8
> > > Mar  7 11:21:18 corn kernel: [182530.140155] usblp0: removed
> > > Mar  7 11:21:18 corn kernel: [182530.375701] usb 5-4: USB disconnect, address 5
> > > #power resumes
> > > Mar  7 11:21:21 corn kernel: [182533.121591] usb 5-3: new high speed USB device using ehci_hcd and address 9
> > > Mar  7 11:21:21 corn kernel: [182533.179788] hub 5-0:1.0: unable to enumerate USB device on port 3
> > > Mar  7 11:21:30 corn kernel: [182542.755370] __ratelimit: 4 messages suppressed
> > > Mar  7 11:21:30 corn kernel: [182542.755379] Buffer I/O error on device dm-15, logical block 8210
> > > Mar  7 11:21:30 corn kernel: [182542.755384] lost page write due to I/O error on dm-15
> > [snip]
> > > Mar  7 11:43:33 corn kernel: [183938.589854] nfsd: last server has exited
> > > Mar  7 11:43:33 corn kernel: [183938.614722] nfsd: unexporting all filesystems
> > > </log>
> >
> > Why are you using device names instead of labels or UUIDs?
> /dev/sdc (or sdd on power resume) is what the kernel is handing me; is
> there a way to change that?
>
> My understanding is that LVM uses UUID's, which makes its failure to
> recover a  bit more puzzling to me.
>
> I suspect I'm not fully understanding the question.

You appear to understand the question...   :)

Re-reading your post, I see, "for a moment".  How much of a moment? 
 IOW, does the machine go down, or just the external enclosure?  If 
just the enclosure, then the kernel probably thinks that the 
external drives are still there.

That leads to these questions:

1. Is the LV made up of both external *and* internal drives,
   or just external?

2. When the power flickers, do you do this:
   # lvchange -an ${VG}/${LV}
   # vgchange -an ${VG}
   [unplug/wait/replug the enclosure]
   # vgchange -ay ${VG}
   # lvchange -ay ${VG}/${LV}

--
I prefer banana-flavored energy bars made from tofu.