Testing The BCache SSD Cache For HDDs On Linux 4.8

First up with some random writes via Flexible I/O Tester, the BCache writeback mode was the fastest. Writeback is known to be the fastest caching mode and writes data first to the SSD then copies it to the HDD backign device asynchronously. With the writethrough mode, data is sent to both the SSD and HDD at the same time but isn't complete until the write finishes on the HDD. With writearound, data is only written to the HDD and treated as a read-only caching mode. With the BCache writeback results the performance was much faster than the standalone Hitachi HDD but much slower (about a quarter the speed) of the Samsung 850 EVO 120GB SSD by itself.

With sequential writes via FIO, the writeback mode was almost twice the speed of the HDD by itself but still a fraction of the speed of SSD-only storage.

For SQLite, the BCache caching was able to beat the older Intel SATA 3.0 SSDSC2BW12 when in the writeback mode. Writeback with discard enabled was slightly faster than with it disabled.