Hi.
On 13.09.2012 15:51, Alexander Motin wrote:
Problem of on-disk metadata garbage is not limited to GEOM_RAID. For
example, I had case where remainders of old UFS file system were found
by GEOM_LABEL and ZFS incorrectly attached to it instead of proper GPT
partition, making other partitions inaccessible. Does it mean we
should remove GEOM_LABEL also? I don't think so. All what GEOM_RAID is
guilty in is that it was not in place for 9.0 release. If we remove it
now, it will just postpone the problem for later time or will never be
able to add it again because of the same reasons.
Unlike GEOM_LABEL, metadata of GEOM_RAID is quite easy to delete
without complete disk erase: `graid status -ag`, `graid delete ...`.
Yes, it can be a problem if system can't boot, but now we at least
have live mode on installation images, that should allow to do it.
Adding some loader tunables indeed could simplify recovery in case of
boot problem. I will probably add such ones now. It won't hurt. But I
disagree they should be disabled by default, limiting users who really
want to use BIOS RAID. Disabling them will also make metadata removal
without full wipe more difficult because different RAIDs have
different on-disk metadata layout, and you should know where exactly
to apply dd.
From my point of view, the policy of new features should be like that:
new features introduced to the system should by default try to mimic the
old behavior. Right now we will have a situation when most of the users
will just upgrade to the new kernel, and will get a non-bootable system
or a system with one 100% busy disk (for example degraded raid0 gives
this). On a system that manages to boot up 'graid delete -f' could lead
to a livelock (got it today, on a degraded raid1). Furthermore, the
situation when the engineer forgot about a disk with a glabel/gmirror
data is less probable than a situation when you have a 'new' disk from
another department which was extracted from some windows server or
workstation. Should I test all of the disks against graid labels ? Yeah,
may be. But for X last years I didn't do that, just because it worked
for me and it didn't lead to a crash. The softraid labels were harmless
all the way. I could use a zpool or a gmirror without even knowing that
I have them. Now I suddenly need to care about the labels. Is GEOM_RAID
great, as a feature ? Yep, it is. Is the way it is introduced into the
system that great ? Not at all.
From my point of view GEOM_RAID in GENERIC kernel is a bomb, and we
will lose lots of FreeBSD beginners due to this.
Eugene.
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