On 05/12/13 12:53, Rob Landley wrote:
On 05/10/2013 09:04:44 AM, David Oostdyk wrote:
Hello,
I have a few relatively high-end systems with hardware RAIDs which
are being used for recording systems, and I'm trying to get a better
understanding of contiguous write performance.
...
The question is, is it possible that high-speed I/O to these hardware
RAIDs could
actually be CPU-bound above ~1400MB/sec?
In some setups your processor is calculating CRCs for the data. It's a
fairly cheap operation, but a cheap operation on gigabytes of data can
still saturate your memory bus.
Rob
At what level would you say this calculation is being applied? Somewhere
in the block/filesystem layer, or in the device driver, or at the
hardware level? I'm seeing write speeds that are about 1/4 the memory
bandwidth of a single thread, which would suggest at least one
"additional" pass through the data before it gets DMA'd out.
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