On Mar 10, 2008, at 0:27, Oliver Martin wrote:
Hmm. Stripe alignment of the beginning of a file system would seem to make sense. Otherwise, even if I tell the file system the stripe size, how should it know where it's best to start writes? If my stripes are 128KB, and I tell the fs, it can make an effort to write 128KB blocks whenever possible. But if the fs starts 64KB into a 128KB stripe, every 128KB write will cause two RMW cycles. At least, that's how I understand it. Maybe there's something else involved and it really doesn't make a difference?
That's exactly what I ment sorry for not being clear enough.If you have a chunk size of 128KB it makes sense to align the beginning of the PV to this as well. Since the header is 64KB itself you should use a --metadatasize of 64 so it becomes 128K. I used a chunk size of 256K so I set the metadatasize to 192 (256-64). You can also use that if you want.
That said, I did not see a big difference when running the benchmarks. A good way to see where the PE starts is pvs -o+pe_start Kind regards, Michael
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