John Stoffel wrote:
"Bill" == Bill Davidsen <davidsen@xxxxxxx> writes:
Bill> John Stoffel wrote:
Why do we have three different positions for storing the superblock?
Bill> Why do you suggest changing anything until you get the answer to
Bill> this question? If you don't understand why there are three
Bill> locations, perhaps that would be a good initial investigation.
Because I've asked this question before and not gotten an answer, nor
is it answered in the man page for mdadm on why we have this setup.
Bill> Clearly the short answer is that they reflect three stages of
Bill> Neil's thinking on the topic, and I would bet that he had a good
Bill> reason for moving the superblock when he did it.
So let's hear Neil's thinking about all this? Or should I just work
up a patch to do what I suggest and see how that flies?
If you are only going to change the default, I think you're done, since
people report problems with bootloaders starting versions other than
0.90. And until I hear Neil's thinking on this, I'm not sure that I know
what the default location and type should be. In fact, reading the
discussion I suspect it should be different for RAID-0 (should be at the
end) and all other types (should be near the front). That retains the
ability to mount one part of the mirror as a single partition, while
minimizing the possibility of bad applications seeing something which
looks like a filesystem at the start of a partition and trying to run
fsck on it.
Bill> Since you have to support all of them or break existing arrays,
Bill> and they all use the same format so there's no saving of code
Bill> size to mention, why even bring this up?
Because of the confusion factor. Again, since noone has been able to
articulate a reason why we have three different versions of the 1.x
superblock, nor have I seen any good reasons for why we should have
them, I'm going by the KISS principle to reduce the options to the
best one.
And no, I'm not advocating getting rid of legacy support, but I AM
advocating that we settle on ONE standard format going forward as the
default for all new RAID superblocks.
Unfortunately the solution can't be any simpler than the problem, and
that's why I'm dubious that anything but the documentation should be
changed, or an additional metadata target added per the discussion
above, perhaps "best1" for best 1.x format based on the raid level.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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