Please forgive me for probably a very stupid question. But why is
FreeBSD so sensitive to filesystem errors that it ends up with panics
like 'freeing free block' or 'ffs_valloc: dup alloc'? I just can't
get it. Failed to allocate vnode? Go allocate another one! Freeing
free block? Leave it free then! I understand these situations should
never happen, but the hell why is it required to panic and kill
everything that would be working happily even if something very
disasterous happen to /backup partition, in example?
Probably because UFS is not designed to be a backup file system but a
working one :)
All those errors indicate file system corruption. To protect other
data from getting corrupted (e.g. by invalid pointers or
calculations), the kernel panics.
To protect us against terrorists our government do strange things too ;-)
After panic data *is* getting corrupted anyway - MySQL tables that were
open are broken, soft-updates are unsync'ed etc etc.
Server is required to reboot, fsck, time is wasted while this occurs.
Why all this should happen because of a single vnode fail? Why not just
throw message in /var/log/messages, return "oh, I failed to save a file"
to the process that initiated the operation and just go on? Are
consequences of attept to "free already free block" *so* dangerous that
it is needed to give up on EVERYTHING? Let's say it was not /backup
partition, ok, it was /var/tmp/some-php-session or even
/var/cron/tabs/someuser file that failed. So what? Even
/boot/kernel/kernel corruption is not critical if you are not going to
reboot right now (or if you have /boot/kernel.old :)
Is there a way to say "Dear kernel, don't panic, I'am holding your hand,
keep working please-please-please?" If so, can it lead to complete
filesystem corruption indeed or it is not so serious?
Thanks.
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