On Wed, Dec 23 2015, Marc Smith wrote: > Solved... appears it was the write-intent bitmap that caused the > performance issues. I discovered if I left the test running longer > than 60 seconds, the performance would eventually climb to where I'd > expect it. I ran 'mdadm --grow --bitmap=none /dev/md0' and now random > write performance is high/good/stable right off the bat. Keeping a write-intent bitmap really is a good idea. Using a larger bitmap chunk size can reduce the performance penalty and preserve much of the value. It is easy enough to experiment with different sizes. NeilBrown
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