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I have installed bcache on ubuntu14.04, 100G ssd, 1T hdd. and I had a performance test with fio randwrite. At beginning, the speed was good, but then it slowed down.

I checked the io status with iostat, it showed that data was being written into hdd from ssd. Both ssd and hdd was busy. This may be the reason why the speed slowed down.

What I can think of is to limit writeback rate, so that the ssd can accept more write requests.

But how to limit writeback rate?

Carl Li
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1 Answers1

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You can use /sys/fs/bcache/*/bdev*/writeback_rate to limit it. 0 turns limitation off as far as I know, higher values increase the rate.

hurikhan77
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