Mark Hahn wrote:
hardware. I/O processors like the Intel IOP333
(http://www.intel.com/design/iio/docs/iop333.htm) contain an xor
engine for raid5 and raid6 calculations, but currently the md driver
does not fully utilize these resources.
the worst insult in the linux world is "solution in search of a problem".
that applies here: are you sure that there is a problem? yes, offload
can be a lovely thing, but it often falls behind the main driver of the
industry - host cpu performance. unless you're specifically targetting
a high-IO device with very little CPU power, I think you'll find a lot
of skepticism about IO coprocessors.
I have a server that can do the raid5 checksum at 8 GB/s, and have no
reason to ever want more than ~100 MB/s on that machine. do I care
about "wasting" 1/80th of the machine? not really, even though it's
a supercomputing cluster node. for fileservers, I mind even less
wasting CPU using the host for parity, since the cycles aren't going
to be used for anything else...
I think that the above holds for server applications, but there are lots
of places where you will start to see a need for serious IO capabilities
in low power, multi-core designs. Think of your Tivo starting to store
family photos - you don't want to bolt a server class box under your TV
in order to get some reasonable data protection ;-)
In the Centera group where I work, we have a linux based box that is
used for archival storage. Customers understand why the cost of a box
is related to the number of disks, but the strength of the CPU, memory
subsystem, etc are all more or less thought of as overhead (not to
mention that nasty software stuff that I work on ;-)).
In this kind of environment as well, finding an elegant way to take
advantage of the capabilities of the new system on a chip parts is a win.
Also keep in mind that the Xor done for simple RAID is not the whole
story - think of compression offload, encryption, etc which might also
be able to leverage a well thought out solution.
ric
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