Raid not shutting down when disks are lost?

[Pierre Ossman <pierre-list@ossman.eu>]

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Today one RAID6 array I manage decided to lose four out of eight disks.
Oddly enough, the array did not shut down but instead I got
intermittent read and writer errors from the filesystem.

It's been some time since I had a failure of this magnitude, but I seem
to recall that once the array lost too many disks, it would shut down
and refuse to write a single byte. The nice effect of this was that if
it was a temporary error, you could just reboot and the array would
start nicely (albeit in degraded mode).

Has something changed? Is this perhaps an effect of using RAID6 (I used
to run RAID5 arrays)? Or was I simply lucky the previous instances I've
had?

Related, it would be nice if you could control how it handles lost
disks. E.g. I'd like it to go read-only when it goes in to fully
degraded mode. In case the last disk lost was only a temporary glitch,
the array could be made to recover without a lengthy resync.

Rgds
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     -- Pierre Ossman

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