Re: GEOM_RAID in GENERIC is harmful

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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