Attempting To Try Out BCache On The Linux 4.1 Kernel

[Soul_keeper]

I noticed you had 16GB of mem for the test system and were doing 8GB set sizes.
A test system with 4GB instead would better isolate the media. The most accurate results seem to come from 2x or more set size which takes forever unless you have low system mem.

[george.yanev]

At the end of the post there's a link that can shed some light regarding bcache behavior. In a nutshell bcache avoid sequential IO operations passing them directly to the HDD. When configured with the following options

echo 0 > /sys/block/bcache0/bcache/sequential_cutoff
echo 0 > /sys/fs/bcache/<cache set>/congested_read_threshold_us
echo 0 > /sys/fs/bcache/<cache set>/congested_write_threshold_us

the data start to be written first to the SSD device before migrating to the HDD (testing with dd), thus the speed is the same as with the stand alone SSD (tested the SSD speed with dd separately to confirm this)

https://www.kernel.org/doc/Documentation/bcache.txt

[Anarchy]

I have a bcache setup 1.5TB hdd and 100GB ssd. On average, the speedup is 2 times from the mean hdd speed. From what I've seen it works the best with small files and with largish files that are often updated. Sometimes it's even faster.

I probably could extract a lot more performance out of my setup, it's just I'm too lazy to read the cache docs. I'm fine with the current performance as it is.