On Thu, 26 Jun 2008, Peter T. Breuer wrote:
"Also sprach Merlin Moncure:"
The linux software raid algorithms are highly optimized, and run on a
I can confidently tell you that that's balderdash both as a Linux author
and as a software RAID linux author (check the attributions in the
kernel source, or look up something like "Raiding the Noosphere" on
google).
presumably (much faster) cpu than what the controller supports.
However, there is still some extra oomph you can get out of letting
the raid controller do what the software raid can't...namely delay
sync for a time.
There are several design problems left in software raid in the linux kernel.
One of them is the need for extra memory to dispatch requests with and
as (i.e. buffer heads and buffers, both). bhs should be OK since the
small cache per device won't be exceeded while the raid driver itself
serialises requests, which is essentially the case (it does not do any
buffering, queuing, whatever .. and tries hard to avoid doing so). The
need for extra buffers for the data is a problem. On different
platforms different aspects of that problem are important (would you
believe that on ARM mere copying takes so much cpu time that one wants
to avoid it at all costs, whereas on intel it's a forgettable trivium).
I also wouldn't aboslutely swear that request ordering is maintained
under ordinary circumstances.
which flavor of linux raid are you talking about (the two main families I
am aware of are the md and dm ones)
David Lang
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