External USB disk doesn't remount after suspend/resume

Prashant Vaibhav pvaibhav at freebsd.org
Wed Jun 24 20:19:46 UTC 2009

I've come across a problem running -CURRENT snapshot from June 12 (and
searching the mailing list for messages after this hasn't yielded anything
I'm running SMP kernel on UP machine, booting from an external usb hdd. The
system suspends and resumes fine, except for one problem. Initially on boot
the external drive is brought up as "umass0" and attached to "scbus1",
however after resuming, the drive is brought up as umass1 and gets attached
to scbus2. Obviously this confuses the system as my root is mounted from
umass0. Thus everything works (ie. I was able to check dmesg for these
messages) that doesn't need access to the filesystem, but since the root
filesystem has disappeared from under us, nothing else works, not even a
'shutdown now' or 'halt' or trying to remount root via 'mount' command. I
was unable to capture a dmesg log because of this.
Is this a known issue, and is there a workaround?  It should be noted that I
have to set "kern.cam.scsi_delay=10000" in loader.conf before the kernel can
mount root from the external usb drive.

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