[SOLVED] USB 2 Slow Writes

Question

I have a external harddisk, the harddisk itself is capable of speeds >100 MB/s (as seen on another machine usb 3), but on my computer, I only get ~10 MB/s write speeds on arch even though the same disk, same port gets ~25 MB/s write speeds on windows. Read is fine at about 30 MB/s which is what I would expect from usb 2
I don't know where to start when it comes to resolving this. I tried googling but only got found results for failing drivers / dealing with usb 2 speeds etc.
Does anyone know why I might be getting slow write speeds or can point me in the right direction?
Edit: I'm running 64 bit version of arch on an acer aspire m1900
Last edited by BennyBolton (2014-07-23 21:18:19)

Answer 1

hmm...
Running again using the command
dd if=save.img bs=4096 count=250000 of=/dev/sdg1
I get the output (while running watch -n 5 kill -USR1 '`pidof dd`'):
157501+0 records in
157501+0 records out
645124096 bytes (645 MB) copied, 3.94887 s, 163 MB/s
200350+0 records in
200350+0 records out
820633600 bytes (821 MB) copied, 8.95875 s, 91.6 MB/s
240618+0 records in
240618+0 records out
985571328 bytes (986 MB) copied, 13.9754 s, 70.5 MB/s
250000+0 records in
250000+0 records out
1024000000 bytes (1.0 GB) copied, 32.1618 s, 31.8 MB/s
250000+0 records in
250000+0 records out
1024000000 bytes (1.0 GB) copied, 32.1619 s, 31.8 MB/s
No idea why it spikes at the beginning (doesn't do this with bs=512) , but the gap in between the following prints show the expected ~30 MB/s, and still stranger, when re-mounting and using dd to copy a file, I get ~10 MB/s with bs=512, but suprisingly ~50 MB/s with bs=4096. If anyone can think of a reason for this behaviour I would be interested to know
Anyways, thanks for the heads up lucke, marking as solved