hi all-
i've got one i've been tearing my hair out over here, and even after
finding some information out there, i'm still totally lost. this may
take a while to explain, so please bear with me.
I've got 2 80GB SATA drives in my FreeBSD machine, which are mapped as
/dev/ad4 and /dev/ad6. I've got 5_STABLE installed on 1 drive, and my
plan is to get a working install of 6_STABLE on the other drive, so i
can take my time to work out the kinks with the upgrade on the 2nd drive
(it hasn't been straighforward) and be able to switch back to my working
5_STABLE machine as needed. That's the plan, anyway.
So I followed the general instructions here:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/faq/book.html#NEW-HUGE-DISK
to clone drive 1 over to drive 2. very cool, no problems, i can pick
either drive in the bootloader and boot up there. so all is well and
good until i boot into drive 2 and start the upgrade process. I realize
the /dev/ad4 and /dev/ad6 are not exactly fixed. It seems almost
arbitrary which drive ends up mapped as /dev/ad6 and /dev/ad4, and this
caused me to nearly munge all of the data on the working 5_STABLE
install before i caught myself. If i boot into drive 1 at boot time,
everything ends up being mounted at /dev/ad6. If i mount into drive 2 at
boot time, the same thing happens. Mind you, i /did/ check /etc/fstab to
ensure that all was well, but i ended up with a weird situation where,
say, / would be /dev/ad4s1a and all of the other mountpoints were at
/dev/ad6*. ugh. confusing!
I found this page, which explains the problem /somewhat/:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/install-steps.html
but to be completely honest, the concept didn't stick. What i need help
with, since these drives are exactly the same size and make, is how i
can do the following:
1) determine the relationship between Drive 1/Drive 2 and ad4/ad6
2) determine exactly which physical drive i am working on at any given
time, since the /dev node mappings seem to be malleable
Drive 0/Drive 1 always refer to the same devices, as FreeBSD ignores the
BIOS mappings (which may change, as outlined in the above docs). These
drive numbers are assigned based on physical controller/device numbering and
addressing, and thus won't change unless you physically change device IDs or
move cables around.
However, once booted, FreeBSD, however, may assign different controller/disk
IDs to the physical devices, depending on what order the devices are
detected. Usually this is static, but in some cases, it is not.
3) enable an environment where i can safely and surely boot into either
drive and know for a fact that the right partitions are mounted ( all of
the data on all of the partitions aside from / is mirrored, so it's
practically impossible to tell which drive is which )
Compile custom kernels on both systems that contain options ATA_STATIC_ID.
This will force the FreeBSD device names to always map to the same physical
controller/drive number.
4) (bonus points) My bootloader shows the following on boot:
F1: FreeBSD
F2: FreeBSD
F5: Drive 1
a) I've only got 1 FreeBSD install on this drive, so what is F2? It just
beeps at me when i try it
F2 represents a slice (in DOS terms, partition) on Drive 0 that is marked
bootable. The reason you get a beep is because there is no boot loader on
that slice.
b) I assume that F5: Drive 1 means that the drive i'm staring at the
options for is Drive 2, adn that selecting F5 will toggle to Drive 1?
Drivers are numbered from 0. So F1/F2 refer to bootable slices on Drive 0.
Regards,
--
Matt Emmerton
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