You're missing my point, it is not about the writes at all, rootfs is much faster on writes, but that does not matter when we're talking about executable code . Is is all about the read operations, and there is where rootfs is not only slower, but consumes 90% CPU time to achieve that slowness. BTW the reason i choose 95MB file to do the read test was to get rid of cache/buffers/whatever effects on the speed. Also have in mind that there is no performance penalty for doing random reads on flash (i.e. /opt) it is only write operations that are affected. Nah, there is no such thing like compression chip, it is the standard ubifs de/compression and it uses CPU. I definitely say it is slower, as my test ( the "time cat" one) shows the maximum reading speed achieved when there is noone else using the CPU. Imagine what happens with that speed when there are several processes using the CPU. The case is closed for me, expect a new update (hopefully today) which moves Qt back to /opt.