Adam Goryachev wrote, On 17.04.2013 03:35:
Obviously, if they suffered a two disk failure then they won't be here
asking for help will they:)
Wrong, sadly. I suffered a 1 disk failure, and I am here asking for
help. And nobody can give it.
Again: I have a RAID5, and 1 (one) disk failed, so I should be fine, but
I cannot read the data anymore, no way to get at it. That's because md
ejected a good (!) drive to start with, and refuses to take it back (!).
(And then another drive failed during resync.) If you have a way, please
do show me, see thread 'Disk wrongly marked "spare", need to force
re-add it'
The problem isn't double disk failure. The problem is bugs in md
implementation.
The Linux kernel advises Linux md that the block
device is gone, so Linux md discards the block device and stops trying
to use it. Personally, I don't see that Linux md has a lot of choice in
the matter
True. But often, such errors are temporary. For example, a loose cable.
I must be able to re-add the device as a good device with data. But I
can't, md doesn't let me.
My case was even more unbelievable: md ejected perfectly good drives
simply because I upgraded the OS. (This happened with 2 independent
arrays, so not coincidence.)
Also, a single sector being unreadable/unwritable doesn't count as "disk
failure" in my book, and shouldn't eject the whole disk. If I have 2
sectors on 2 different disks that are unreadable, md currently trashes
the whole array and doesn't let me read anything at all anymore. That's
obviously broken, but unfortunately the sad reality.
See http://neil.brown.name/blog/20110216044002#1
(And, BTW, RAID6 doesn't really help with this problem, because it's
quite possible that 3 disks have sectors unreadable/unwritable.)
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