I have a USB key (PQI U822V-Speedy 32G) that I am trying to benchmark quick'n'dirty on Linux. I'm testing write bandwith.
dd on raw partition
I created a partition starting at sector 2048, then did a 4 GB sequential write:
dd if=/dev/zero of=/dev/sdb1 bs=1M count=4096
I get ~22 MB/s.
I also tried several (4)
dd running in parallel like the one above but using
count=1024 and the
seek= option to write to different areas of the drive. Same results.
dd on filesystem
However, when I format the
sdb1 partition with either
NTFS, and copy big files to it (either real or
/dev/zero), like this:
time dd if=/dev/zero of=/media/USBKEY/file.bin bs=1M count=4096 ; time sync
I do achieve > 66 MB/s as advertised by the manufacturer. Of course, I considered the
sync duration just after the copy.
Why is there such a big performance difference?