si-ghan-bi wrote:Before thinking the worst, why don't you try a real benchmark? The iostat command is not what you need to have reliable values: for example, it gives you average values and if you are not using the disk heavily, values are off.
I was writing data to the disk at 5-7MB/s and other benchmark apps and "time dd ..." showed the same or worse with compression and spotlight off so it does not skew the numbers. I am remaking the pool in about 15 hours (the time it takes to move everything off) and if it still shows bad (single digit) numbers I will have drop ZFS for good since I store video on it that I can't watch unless I cache the whole thing or save to desktop first. There is simply no logical reason why a 4 disk array should be slower than a single disk over USB3.
The disks are in use so these numbers are skewed, a lot, but I will test writing and benchmarking again before destroying the pool.
*Writes using dd...
1 HFS+ disk --- 25.3MB/s
3 ZFS RAIDz --- 5.4MB/s
si-ghan-bi wrote:And more important: are there disadvantages in using the ashift command?
None that I have found, it is there to increase performance. It could reduce capacity but with the gain by compression the little that is lost is easily gained back. Of course my compression is off to get back speed.