Monday 15th April 2013: 6.36pm. Link shared: https://plus.google.com/109885711759115445224/posts/Ltn4JzAS9LX
Finally got my mSATA USB 3.0 enclosure which I had to order from the US. With a Crucial M4 mSATA SSD inserted, my Samsung ARM Chromebook gets:
iozone -e -I -a -s 1000M -r 4k -r 512k -i 0 -i 1 -i 2
random random bkwd record stride
KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
1024000 4 10509 11524 11235 11548 9039 11808
1024000 512 38881 39764 40345 40290 39491 38930
In other words, about 10Mb/sec for 4k reads and writes with no real difference if they're random. And a peak transfer rate of ~38Mb/sec, also with no real difference if it's random. All these suggest it's the USB 3.0 controller which is getting in the way. These results were expected of course (see https://plus.google.com/109885711759115445224/posts/Ltn4JzAS9LX).
If there ever was an example of USB 3.0 controller limited performance, it is the above: Samsung's Exynos 5 ARM chipset's USB controller really is not great. That SSD should hit 250Mb/sec reads over USB 3.0 :(