[Discuss] Hybrid drives and Linux?

[Richard Pieri]

Tom Metro wrote:
> What I read prior to buying was that the speed improvement wasn't that
> dramatic. It was a minor cost premium, so I went for it.

I've done some limited comparisons between plain disks, hybrid disks and 
Intel SRT. Hardly anything scientific, just the same computer with 
different disks and configurations.

The best performance in general cases is a plain flash-based SSD. In 
specific cases, notably sustained writes of uncompressable data like 
video and music files, I/O performance drops to somewhere between 
terrible and atrocious.

Second best overall is Intel SRT with flash SSD cache with either 
conventional or hybrid disk. Boot times are almost as good as the raw 
SSD. Other activities are hit or miss depending on random vs. sustained 
I/O. I've not noticed any significant differences with double-caching 
(hybrid + SSD).

Third is the hybrid disk on its own. Boot times are faster than a 
conventional disk but not quite as fast as ISRT, which may have more to 
do with the size of the cache than anything else. Other activities are 
even more of a hit/miss deal because of the much smaller flash cache, 
typically 8GB compared to 30-60GB under ISRT.

The one drawback to IRST is that it bonds a single rotating disk to a 
single SSD. Two drawbacks, the second is that it is only for Windows. 
I've not used Linux bcache but since it works similarly to IRST it 
should perform similarly modulo cache performance optimizations that are 
still being tuned.

Best bang for the buck? A 5400 RPM disk and a 32GB SSD for cache.

-- 
Rich P.