Hello,
I've had good results with bcache in the past, so I recently tried to
use it to accelerate loading times of Steam games.
Tthe results I got were rather surprising. When using bcache, in several
cases performance was up to 1.5 worse than when using only the HDD and
up to 4 times worse than when running only from SSD. Results were
consistent over 10 sequential runs (less than 10% deviation in load
times), so the cache should be hot.
I used the same harddrives for bcache, plain HDD and plain SSD
(though different partitions).
I also enabled writeback and set the sequential_cutoff to zero
(expecting this to be almost equivalent to using the SSD directly).
The cache size is 32 G, and the backing device is 128 G. However, I am
pretty sure that all the data that is read fits into the cache
completely (but I'm not sure how to confirm this).
Does anyone have any insight what could cause this? I'm not expecting
bcache to always match performance of using plain SSD, but I would have
expected it to not make things worse than using a plain HDD....
Tested on Ubuntu cosmic with kernel 4.18.
Best,
-Nikolaus
--
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
