On Mon, 2015-07-13 at 15:37 -0600, jd1008 wrote:
On 07/13/2015 03:13 PM, Patrick O'Callaghan wrote:
> On Mon, 2015-07-13 at 13:50 -0600, jd1008 wrote:
> > I started a tar command from
> > one external eSATA drive (ext4), connected to eSATA port,
> > out to a USB flash drive (with vfat). The USB stick is touted
> > to support 50MB/s write, 160MB/s read.
> Have you actually measured its real write speed for large files?
> Try
> something like:
>
> time dd if=/dev/zero of=/the/usb/drive count=1000 bs=1M
>
> You might be surprised.
>
> poc
Well, I am not surprised, but disappointed (seriously!!!)
$ time dd if=/dev/zero of=/run/media/jd/USB3_ST1-2K/test-wr-speed.txt
bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 57.6116 s, 18.2 MB/s
real 0m57.88s
user 0m0.00s
sys 0m1.28s
So much for 50MB/s write speed!!!!
USB flash drives only work efficiently at multiples of their internal
block size, which is not usually directly visible to the host (Google
for info on how flash drives actually work; hint: every write requires
the entire block to be zeroed and then overwritten). The claimed I/O
speed of these devices is achievable, just not under real conditions
with a generic driver.
poc