Hi,

 This is an issue on FreeBSD, but not Solaris. 

 It works as I expect on a Solaris 11.3-BETA machine. 

 A file in the root of a zfs dataset doesn't seem to take the set recordsize, yet if I create a sub-dataset, it does.

 Perhaps I am not using zdb correctly to examine the file in the root, as it's displaying like it's a DSL Directory, not a ZFS Plain File, but if that's the case, then zdb's switches are different for FreeBSD than from Solaris. 

 This behaviour has existed for a while, for all the 10.x's I'm quite sure, and still happens today on a 10.2-p7 RELEASE machine. 

 Example:

# zpool create pool92_1 da1 da11 da9 da12 da13 da14
# zfs set recordsize=64k pool92_1
# zfs get recordsize pool92_1
NAME      PROPERTY    VALUE    SOURCE
pool92_1  recordsize  64K      local

# cd /pool92_1
# dd if=/dev/random of=./test_file bs=1M count=12
12+0 records in
12+0 records out
12582912 bytes transferred in 0.325594 secs (38645997 bytes/sec)

# ls -i
8 test_file

# zdb -dd pool92_1 8  
Dataset mos [META], ID 0, cr_txg 4, 144K, 45 objects

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
         8    1    16K    512      0    512    0.00  DSL directory

# zfs get recordsize pool92_1
NAME      PROPERTY    VALUE    SOURCE
pool92_1  recordsize  64K      local

# zfs create pool92_1/folder
# zfs get recordsize pool92_1/folder
NAME             PROPERTY    VALUE    SOURCE
pool92_1/folder  recordsize  64K      inherited from pool92_1


# cd folder
# dd if=/dev/random of=./test_file bs=1M count=12
12+0 records in
12+0 records out
12582912 bytes transferred in 0.384501 secs (32725305 bytes/sec)

# ls -i
8 test_file
# zdb -dd pool92_1/folder 8
Dataset pool92_1/folder [ZPL], ID 49, cr_txg 44, 12.1M, 8 objects

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
         8    3    16K    64K  12.0M  12.0M  100.00  ZFS plain file


The full dumps if you're interested are:

# zdb -dddd pool92_1 8
Dataset mos [META], ID 0, cr_txg 4, 126K, 52 objects, rootbp DVA[0]=<2:446000:1000> DVA[1]=<3:443800:200> DVA[2]=<4:408000:200> [L0 DMU objset] fletcher4 lz4 LE contiguous unique triple size=800L/200P birth=60L/60P fill=52 cksum=be53af6aa:46998543bc9:d8c388544dcd:1cb577de44fcab

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
         8    1    16K    512      0    512    0.00  DSL directory
                                        256   bonus  DSL directory
        dnode flags: 
        dnode maxblkid: 0
                creation_time = Wed Nov 18 11:59:47 2015
                head_dataset_obj = 0
                parent_dir_obj = 2
                origin_obj = 0
                child_dir_zapobj = 10
                used_bytes = 0
                compressed_bytes = 0
                uncompressed_bytes = 0
                quota = 0
                reserved = 0
                props_zapobj = 9
                deleg_zapobj = 0
                flags = 1
                used_breakdown[HEAD] = 0
                used_breakdown[SNAP] = 0
                used_breakdown[CHILD] = 0
                used_breakdown[CHILD_RSRV] = 0
                used_breakdown[REFRSRV] = 0

# zdb -dddd pool92_1/folder 8
Dataset pool92_1/folder [ZPL], ID 49, cr_txg 44, 12.1M, 8 objects, rootbp DVA[0]=<2:443000:1000> DVA[1]=<3:442800:200> [L0 DMU objset] fletcher4 lz4 LE contiguous unique double size=800L/200P birth=60L/60P fill=8 cksum=b55f2d725:46568e61db8:e07315731014:1eacd8bf5cb44a

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
         8    3    16K    64K  12.0M  12.0M  100.00  ZFS plain file
                                        168   bonus  System attributes
        dnode flags: USED_BYTES USERUSED_ACCOUNTED 
        dnode maxblkid: 191
        path    /test_file
        uid     0
        gid     0
        atime   Wed Nov 18 12:03:10 2015
        mtime   Wed Nov 18 12:03:10 2015
        ctime   Wed Nov 18 12:03:10 2015
        crtime  Wed Nov 18 12:03:10 2015
        gen     47
        mode    100644
        size    12582912
        parent  4
        links   1
        pflags  40800000004


On a Solaris 11.3-BETA machine, here's what I see:

root@solaris175:~# zpool create pool175 c2t1d0
root@solaris175:~# zfs set recordsize=64k pool175
root@solaris175:/pool175# dd if=/dev/random of=./test_file bs=1073741824 count=120
root@solaris175:/pool175# ls -all
total 267
drwxr-xr-x   2 root     root           3 Nov 18 16:39 .
drwxr-xr-x  27 root     sys           30 Nov 18 16:37 ..
-rw-r--r--   1 root     root      124800 Nov 18 16:39 test_file

root@solaris175:/pool175# ls -i
        10 test_file

root@solaris175:/pool175# zdb -dd pool175 10
Dataset pool175 [ZPL], ID 18, cr_txg 1, 161K, 8 objects

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
        10    2    16K    64K   130K   128K  100.00  ZFS plain file


Yes, there are two differences here (I couldn't use bs=1M for dd, and I only used one disk) between the FreeBSD and Solaris machines, but I feel it's still valid enough to illustrate my point.

I do believe something more than just the reporting is off, as workloads that benefit from recordsize=64k are slower in the root dataset than in a sub-dataset.