I tested simple reading and writing performance using dd on the /home volume which has sufficient space available. I did the testing with a 512 MB file using read/write block size of 1MB. The reading performance gives me about 98 MB/sec which is great. For writing I get only 17.60 MB/sec. For writing I was expecting that the kernel does write behind which should finish immediately because I have 800 MB free memory. I also tried to mount the volume with async or barrier=0 options, no change.
I used the following commands for testing:
# cd /home
For writing:
# time dd if=/dev/zero bs=1024k count=512 of=xx
For reading: (I was rebooting after write to ensure that I don't read cached content)
# time dd if=xx bs=1024k of=/dev/null
I believe the write behind is somehow turned off, but I don't know where. The 17.6 MB is properly what the flash controller can handle.
Any ideas?