Nick Rout wrote: > I have an imation 4G flash drive that is sitting in a USB2 port. I am > transferring a 3.7G file from the computers sata hard drive to the usb > drive. > > It seems to be taking about 20 minutes This seems far too long. USB > data rate 60MB/s. > > 3719MB/60MB/s = 62 seconds, give or take. > > Now I know I won't get a sustained rate anywhere near that, but the > predicted time is 20 odd times over the theoretical minimum time. > > So where should I look for problems. Suspicions centre around: > > 1. USB flash drive cannot handle the data rate, tough one Nick; or > > 2. USB operating at USB1.1 rate only. How would I diagnose that? > > Its an intel based compaq motherboard, excerpts from lspci: > > 00:1d.0 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB > UHCI Controller #1 (rev 02) > 00:1d.1 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB > UHCI Controller #2 (rev 02) > 00:1d.2 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB > UHCI Controller #3 (rev 02) > 00:1d.7 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB2 > EHCI Controller (rev 02) > > dmesg displays a lot of lines with the term USB in them, dunno whats relevant. > Flash devices take a certain length of time to write to the non-volatile cells inside the flash IC. Also, banks of cells have to be erased to make space for more data. Finally, the read access time is MUCH faster than the write and erase time.
It so happens that I have a data sheet for a flash device on my desk... Samsung K9KG08R0B (128 Mbyte NAND flash) Page write cycle time: 200 us Page write size: 512 bytes This means that this particular flash device can write 512 bytes in 200 us = 2.56 bytes/us or about 2.6 mega bytes per second. Block erase time: 2 ms Block erase size: 16K bytes This device can erase 16K bytes in 2ms = 8192 bytes/ms = 8 mega bytes per second Page serial read time: 50 ns Page random read time: 15 us Page read size: 512 bytes This flash device can read pages sequentially at 512 bytes in 50 ns = 10.24 bytes/ns or about 10 giga bytes per second. This flash device can read random page at 512 bytes in 15 us = 34.13 bytes/us or about 34 mega bytes per second. For writing, the flash write time is the limiting factor. For reading, the USB data rate is the limiting factor. I have no idea what flash devices are actually used in USB flash drives. Presumably not this small, old one. Stephen Irons ======================================================================= This email, including any attachments, is only for the intended addressee. It is subject to copyright, is confidential and may be the subject of legal or other privilege, none of which is waived or lost by reason of this transmission. If the receiver is not the intended addressee, please accept our apologies, notify us by return, delete all copies and perform no other act on the email. Unfortunately, we cannot warrant that the email has not been altered or corrupted during transmission. =======================================================================
