On 07/10/16 19:52, Phil Turmel wrote:
Hi DP,
{It's good that you are trimming replies, but don't cut the ID of who
wrote what. }
Oh, yeah, sorry.
You want to push the failure condition from being "broken raid with
likely salvageable data, except for one sector" to "repeated errors to
the upper layers with unknowable corruption as side effects".
That actually describes it pretty well, yes. %) Being able to choose a
failure condition most suitable for your specific situation, and being
able to push it that far and still have a working RAID if you want that.
Then patch your kernel with your desired behavior. "Free software"
doesn't mean someone writes what you want for free. And I disagree with
you, so would object to it being put in the mainline kernel.
Yes, that's one of the things on my TODO list once I become a developer
able to do that. :) I just thought I'm probably not the only one who
wants that, and so I wanted to learn why is it not possible. And listen
to what other people really think about it.
Anyway, if I had a collapsed RAID-5, I would want to at least have an
easy option to start it in a read-only mode in the last-known working
state, while the faulty drives are still not out of sync, and recover
data easily (to my single backup drive), or continue using the array for
a while, manually deleting one "bad" file if necessary; this is of
course not a "good thing" to do, but this way, RAID would be at least
not worse than single drives with faulty sectors, which are capable of
that, while RAIDs are not! I would be fine with that in my archive - as
I'm fine with some less importand parts of the archive being on faulty
single drives. It's just that I don't want to lose the whole drive due
to a hardware failure - and RAID adds more causes other than that,
instead of offering more protection against that.
MD raid has no idea what is at any given sector. And with a
near-infinite variety of layering choices, there's no way it's going to.
That's why *you* have to do this. You trimmed my description of the
only "easy option" actually trustable.
I actually wanted to ask about that. Can you really ddrescue a drive
with a "hole" in it, re-add it and expect it to work?.. What happens if
you try to read from that "hole" again? And while I'm talking about
re-adding, when does it become impossible to "re-add" a drive?..
--
darkpenguin
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