Warren Thanks for the thoughts. Even with 'dmesg', I found nothing. The reboot got rid of the problem and it continues to run perfectly in the same configuration. I, too, have a slight dislike for external USB disks, and much prefer internal drives for esveral reasons: - Internal drives are protected by being inside a tower and thus have less chance of falling or being bumped than free-standing external boxes - Fewer plugs and wires - Power-up sequencing is coordinated with CPU power - SATA3 is faster than USB3 (I think) But sometimes one has no choice. The Mac pro may look cute in its black cylinder, for example, but there's no place to add anything to it. External drives are the only choice that I know of. David At 07:57 AM 1/15/2018, Warren Young wrote: >On Jan 12, 2018, at 3:18 PM, david <david at daku.org> wrote: > > > > Or is it related to the annoying spin-down > and spin-up delay of external USB disks. > >More likely, crap hardware, which is awfully hard to avoid in USB-land. > >Just the other day, I traced a machine that >failed to reboot to an external USB >disk. Unplug it, machine boots right up. Move >the same disk to a machine as different as can >be — different hardware, different OS, different >firmware — and it kernel panic’d that box >within about a minute of plugging it in. >in. > >Then there was the time a USB enclosure ate my >data. Only the filesystem’s strong checksums >saved me that time. I moved the disk to another >enclosure, and the bad sector writes stopped >occurring; all else remained the same. > >The problem is a market conditioned to believe >that it should expect to pay $13.64 for an >enclosure, power supply, and interface cable and >get a 5-star product. If you put a $200 >enclosure in front of the vast majority of >members of that market, they’d either >disbelieve the price or rate it 1 star for bad >value, even if it was guaranteed to outlast the >prevalence of the USB standard it supports, had >a higher transfer rate, and had guaranteed data >corruption rates best given in scientific >notation with large negative exponents. > >Whenever I have a machine with an unkillable >userspace program, I run dtrace, and almost >always get told exactly which bit of hardware >(and therefore which kernel driver) is holding the machine hostage. > >You might be able to dig the same info out of >/var/log/messages, given close-enough timestamps. >_______________________________________________ >CentOS mailing list >CentOS at centos.org >https://lists.centos.org/mailman/listinfo/centos