panic after removing usb flash disk

Kevin Oberman oberman at
Thu Aug 16 10:26:53 PDT 2007

> Date: Thu, 16 Aug 2007 10:08:17 -0700
> From: Jeremy Chadwick <koitsu at>
> On Thu, Aug 16, 2007 at 09:31:32AM -0700, Kevin Oberman wrote:
> > To further complicate things, many of the major contributors to FreeBSD
> > are only interested in it for its use as a server or embedded OS. This
> > means that they are willing to commit resources to SMP, which they need,
> > but not so willing for hot-removal of storage, which is of only slight
> > value in the server and embedded OS world.
> Really?  Hmm.  This got me thinking: it would benefit Juniper greatly if
> they 1) stopped using single disks in their multi-thousand-dollar
> routers (try dual disks with RAID 1), 2) stopped using ATA disks and
> went with SCSI, and 3) put in a hot-swap backplane of some sort.
> Nothing like paying US$20K for a ""enterprise"" product that uses single
> ATA disks with no hotswap capability.  My point is that it WOULD benefit
> some of the major contributors to rank this issue as serious.

I have no idea whether Juniper is a contributor to FreeBSD. Just because
they use it does not mean that they contribute. (Then again, you may
know that they do.)

That said, all of the higher end Juniper boxes really run off Compact
Flash which is ATA. The hard drive is used for backup, distributions,
logging, etc. If properly set up, the system will run fine without a
hard drive. (OK Maybe it limps a bit and you want to get it fixed very

That said, I am quite a ware of the pain caused by hard drive failures
on Junipers. RAID and hot-swap are interesting approaches, but the
ability to pull out a mounted media is probably not too significant. I
hot swap ATA drives in my laptop all of the time. I just umount and use
atacontrol to detach the controller.

In this day of SATA, I'm not sure I see an advantage to SCSI in the
Juniper but there is a need for higher-end drives. They exist in both
3.5 and 2.5 in. form factors and have reliability specs similar to
SCSI. Disk performance is really not an issue for a Juniper router.

> > I am sure that a lot of people who have no professional interest in
> > fixing this do have a strong personal interest and I suspect that it
> > will happen before too long, but complaining about it is not really
> > going to help as almost every FreeBSD desktop and mobile user has been
> > bitten by this at one time or another and wants it fixed.
> The problem is that as computing changes and the hardware evolves, the
> underlying OS design being discussed here has not.  There have been many
> real-life examples given where one cannot do anything about the
> circumstances that induce the panic (USB hub losing power due to a cat
> pulling the AC cord, laptops going into S1/S3 sleep mode, or server
> admins who need to go to the co-lo and perform some realtime data
> copying who simply forgot to umount).

Amen! No argument. I think everyone acknowledges that FreeBSD really
needs to get this fixed. I have tickled this problem in several ways and
it really has a painful bite! (Forgetting to umount a disk on a
server is pretty inexcusable, if human.)
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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