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 -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
