RAID5/6 support for Btrfs
There are many things that the kernel lacks, but RAID implementations is not on
that list. Both the MD and DM subsystems currently have full RAID support,
while the Btrfs filesystem has lower-level RAID support.
has been posted a
couple of times, but has not yet made it into the mainline. So, one might
well be justified in wondering if yet another RAID5 implementation is
needed in the kernel.
There will be one if Boaz Harrosh has his way; his RAID5 support patch has been posted to a few
filesystem-related kernel development lists. Boaz's patch is aimed at
adding RAID5 support to the "objects raid engine" code in the exofs
filesystem, which provides a POSIX filesystem on top of object-storage
devices. It also implements RAID5 for the pNFS object-storage backend.
According to Boaz, this work constitutes a nice, general-purpose RAID
library that could be used in other settings; in particular, he says, Btrfs
could make use of it. What would be even nicer, of course, is if some of
the existing in-kernel RAID implementations could also move to this library -
or if exofs could use one of those implementations. This version of RAID5
support may well be cleaner and more general than the others, but it may
well take a stronger argument than that to get a new RAID subsystem merged
at this point.
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