root@netboot:~# (cd /sys/block/mmcblk0/device/ ; for i in * ; do if [ -f $i ] ; then echo -n "$i: " ; cat $i ; fi ; done)
cid: 02544d534431364760dcbf359a00a800
csd: 400e00325b590000777f7f800a400000
date: 08/2010
fwrev: 0x0
hwrev: 0x6
manfid: 0x000002
name: SD16G
oemid: 0x544d
scr: 02b5800026027102
serial: 0xdcbf359a
type: SD
uevent: DRIVER=mmcblk
MMC_TYPE=SD
MMC_NAME=SD16G
MODALIAS=mmc:block


root@netboot:~# ~/flashbench/flashbench -a /dev/mmcblk0 --blocksize=1024
align 536870912 pre 838µs       on 1.12ms       post 960µs      diff 222µs
align 268435456 pre 859µs       on 1.09ms       post 955µs      diff 186µs
align 134217728 pre 860µs       on 1.1ms        post 957µs      diff 196µs
align 67108864  pre 861µs       on 1.11ms       post 957µs      diff 203µs
align 33554432  pre 860µs       on 1.11ms       post 960µs      diff 197µs
align 16777216  pre 861µs       on 1.11ms       post 953µs      diff 203µs
align 8388608   pre 859µs       on 1.11ms       post 961µs      diff 198µs
align 4194304   pre 863µs       on 1.1ms        post 925µs      diff 211µs
align 2097152   pre 862µs       on 1.11ms       post 965µs      diff 199µs
align 1048576   pre 954µs       on 978µs        post 970µs      diff 15.8µs
align 524288    pre 951µs       on 977µs        post 973µs      diff 14.8µs
align 262144    pre 947µs       on 977µs        post 967µs      diff 19.8µs
align 131072    pre 947µs       on 983µs        post 969µs      diff 25.5µs
align 65536     pre 951µs       on 981µs        post 956µs      diff 26.9µs
align 32768     pre 948µs       on 977µs        post 963µs      diff 21.6µs
align 16384     pre 950µs       on 978µs        post 950µs      diff 27.7µs
align 8192      pre 963µs       on 960µs        post 963µs      diff -3106ns
align 4096      pre 962µs       on 969µs        post 956µs      diff 10.1µs
align 2048      pre 963µs       on 953µs        post 951µs      diff -3893ns

>From which I guess 2M erase block size.  Not sure how to interpret the last 4 rows.

Only 1 open allocation unit by the look of the following :-(

root@netboot:~# ~/flashbench/flashbench --open-au --open-au-nr=1 --erasesize=$[2 * 1024 * 1024] --blocksize=$[256 * 1024] /dev/mmcblk0
2MiB    3.68M/s
1MiB    3.16M/s
512KiB  3.06M/s
256KiB  3.33M/s
root@netboot:~# ~/flashbench/flashbench --open-au --open-au-nr=2 --erasesize=$[2 * 1024 * 1024] --blocksize=$[256 * 1024] /dev/mmcblk0
2MiB    3.09M/s
1MiB    2.01M/s
512KiB  1.43M/s
256KiB  618K/s

root@netboot:~# ~/flashbench/flashbench -f /dev/mmcblk04MiB    2.51M/s  2.46M/s  3.73M/s  3.72M/s  3.72M/s  3.72M/s 
2MiB    3.7M/s   2.46M/s  3.73M/s  3.73M/s  3.72M/s  3.72M/s 
1MiB    3.7M/s   2.46M/s  3.73M/s  3.74M/s  3.72M/s  3.72M/s 
512KiB  3.7M/s   2.45M/s  3.72M/s  3.7M/s   3.73M/s  3.73M/s 
256KiB  3.71M/s  2.63M/s  3.72M/s  3.73M/s  3.72M/s  3.72M/s 
128KiB  3.71M/s  2.82M/s  3.73M/s  3.72M/s  3.72M/s  3.72M/s 
64KiB   3.71M/s  3.01M/s  3.72M/s  3.72M/s  3.72M/s  3.72M/s 
32KiB   3.58M/s  2.73M/s  3.57M/s  3.57M/s  3.58M/s  3.57M/s 
16KiB   2.95M/s  2.25M/s  2.94M/s  2.95M/s  2.94M/s  2.95M/s 

The --scatter-order=<n> --scatter-span=<m>  arguments are not really documented, so I didn't know how I should be using them, so I didn't.  There are some strange outliers on the plot, most of which seem to end up consistently in the same place.

This card has had an HD image file copied over it (with dd) prior to any of these results being generated.