I also just ran some tests on RHEL7 with 2 types of storage.  I'm more
encouraged by these results.  I've been focusing on on-disk layout
improvements, haven't even looked at throughput.  But if ondisk layout
is improved, throughput should follow.

Again, these results are just showing the increased density of extents
in the ondisk layout, collected with command line like:
 find mix_rhel7_sorted -type f | xargs wc -l

1) fusionio iodrive2

   102 rhel7_unsorted/thin_bs512_io128.txt
   102 rhel7_unsorted/thin_bs1024_io1024.txt
    96 rhel7_unsorted/thin_bs1024_io512.txt
    99 rhel7_unsorted/thin_bs256_io512.txt
    17 rhel7_unsorted/rhel7_unsorted.txt
    95 rhel7_unsorted/thin_bs512_io1024.txt
   108 rhel7_unsorted/thin_bs128_io128.txt
    98 rhel7_unsorted/thin_bs512_io256.txt
   645 rhel7_unsorted/thin_bs256_io1024.txt
    94 rhel7_unsorted/thin_bs128_io1024.txt
    97 rhel7_unsorted/thin_bs128_io256.txt
   100 rhel7_unsorted/thin_bs512_io512.txt
    97 rhel7_unsorted/thin_bs256_io256.txt
   261 rhel7_unsorted/thin_bs1024_io128.txt
    97 rhel7_unsorted/thin_bs1024_io256.txt
    99 rhel7_unsorted/thin_bs128_io512.txt
   325 rhel7_unsorted/thin_bs256_io128.txt
  2532 total

   110 rhel7_sorted/thin_bs512_io128.txt
    99 rhel7_sorted/thin_bs1024_io1024.txt
   102 rhel7_sorted/thin_bs1024_io512.txt
   103 rhel7_sorted/thin_bs256_io512.txt
   104 rhel7_sorted/thin_bs512_io1024.txt
    87 rhel7_sorted/thin_bs128_io128.txt
   104 rhel7_sorted/thin_bs512_io256.txt
    99 rhel7_sorted/thin_bs256_io1024.txt
   101 rhel7_sorted/thin_bs128_io1024.txt
   107 rhel7_sorted/thin_bs128_io256.txt
   101 rhel7_sorted/thin_bs512_io512.txt
   103 rhel7_sorted/thin_bs256_io256.txt
   109 rhel7_sorted/thin_bs1024_io128.txt
   107 rhel7_sorted/thin_bs1024_io256.txt
    17 rhel7_sorted/rhel7_sorted.txt
   109 rhel7_sorted/thin_bs128_io512.txt
   117 rhel7_sorted/thin_bs256_io128.txt
  1679 total

2) 4-way dm-stripe on SAS (chunk=64K stripe=256K)

   148 mix_rhel7_unsorted/thin_bs512_io128.txt
   234 mix_rhel7_unsorted/thin_bs1024_io1024.txt
   290 mix_rhel7_unsorted/thin_bs1024_io512.txt
  1118 mix_rhel7_unsorted/thin_bs256_io512.txt
   133 mix_rhel7_unsorted/thin_bs512_io1024.txt
   112 mix_rhel7_unsorted/thin_bs128_io128.txt
   124 mix_rhel7_unsorted/thin_bs512_io256.txt
   103 mix_rhel7_unsorted/thin_bs256_io1024.txt
    95 mix_rhel7_unsorted/thin_bs128_io1024.txt
    98 mix_rhel7_unsorted/thin_bs128_io256.txt
   133 mix_rhel7_unsorted/thin_bs512_io512.txt
    92 mix_rhel7_unsorted/thin_bs256_io256.txt
   139 mix_rhel7_unsorted/thin_bs1024_io128.txt
   249 mix_rhel7_unsorted/thin_bs1024_io256.txt
    96 mix_rhel7_unsorted/thin_bs128_io512.txt
    99 mix_rhel7_unsorted/thin_bs256_io128.txt
  3263 total

   74 mix_rhel7_sorted/thin_bs512_io128.txt
   73 mix_rhel7_sorted/thin_bs1024_io1024.txt
   75 mix_rhel7_sorted/thin_bs1024_io512.txt
   65 mix_rhel7_sorted/thin_bs256_io512.txt
   76 mix_rhel7_sorted/thin_bs512_io1024.txt
   84 mix_rhel7_sorted/thin_bs128_io128.txt
   68 mix_rhel7_sorted/thin_bs512_io256.txt
   76 mix_rhel7_sorted/thin_bs256_io1024.txt
   76 mix_rhel7_sorted/thin_bs128_io1024.txt
   75 mix_rhel7_sorted/thin_bs128_io256.txt
   73 mix_rhel7_sorted/thin_bs512_io512.txt
   71 mix_rhel7_sorted/thin_bs256_io256.txt
   72 mix_rhel7_sorted/thin_bs1024_io128.txt
   65 mix_rhel7_sorted/thin_bs1024_io256.txt
   79 mix_rhel7_sorted/thin_bs128_io512.txt
   72 mix_rhel7_sorted/thin_bs256_io128.txt
 1174 total