GEOM gotcha upgrading from 6.x to 7.x
peterjeremy at optushome.com.au
Fri Jun 27 21:49:18 UTC 2008
Yesterday, I planned to try an upgrade from 6.x to 7.x on one of the
servers at work, on the assumption that I could reasonably easily
revert to 6.x if things went bad. My confidence in being able to
do that was severely shaken when I saw "Upgrading metadata" messages
for both geom_mirror disks when the 7.x kernel booted.
Whilst I did not need to revert, some examination of the geom_mirror
source shows that (as I feared), a 6.x kernel will choke on a 7.x
I've looked through the various geom man pages, UPDATING, the relevant
commit message and various mailing lists and am unable to find any
mention of this. Having the kernel automatically alter persistent
state on the host in a way that is incompatible with earlier kernels
is bad enough. Doing so without any mechanism to revert the change
and with no "heads-up" warning of the change is, IMO, unacceptable.
I accept that it's sometimes necessary to make changes that are not
backward compatible or that are difficult to revert, such changes
are normally discussed in advance and come with heads-up warnings.
I can't think of any previous case where simply test booting a kernel
is enough to render your system unusable with an older kernel.
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.
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