Here is some JFFS2 performance numbers using a 150Mhz K61 SOM. In this test, a 120MB partition in the NAND Flash device (128 MB) is allocated to a JFFS2 file system.

Write to a file in a 120MB JFFS2 file system:

~ # dd if=/dev/zero of=/mnt/100m.file bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (100.0MB) copied, 61.909967 seconds, 1.6MB/s

Mount of a 120MB JFFS2 partition containing a 100MB file:

~ # busybox time mount -t jffs2 /dev/mtdblock2 /mnt
real 0m 2.53s
user 0m 0.00s
sys 0m 1.24s

Read of a 100MB file from a 120MB JFFS2 file system:

~ # dd if=/mnt/100m.file of=/dev/null bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (100.0MB) copied, 18.735672 seconds, 5.3MB/s