Inconsistent file copying speeds across USB devices.

BrokenArrows · 14-01-2011 09:02PM #1

Over the past few days on multiple pcs i have had to copy a large amount of data from computer harddrives to a usb harddrive.

I cant understand why the speeds vary so much on the same pcs with the same harddrive.

eg. I start to copy a 12GB file. and the speed starts at 30MB/s and might drop to 5MB/s. If i cancel the transfer and start again it might maintain a constant 20MB/s or it might transfer slower or faster.
The computers are not performing any other task other than copying.

This happens on multiple pcs and multiple USB harddrives.

Any idea how to improve consistency?

Khannie · 14-01-2011 10:52PM

The consistency isn't an issue with the drive. The OS buffers the write in memory somewhat (this is the fast bit, but it's not actually writing at that speed). When that buffer is filled it is forced to actually wait on the disk to flush (this is where you're seeing the drop off). There's no way around this that I'm aware of. On linux you can force a disk flush with the "sync" command. Not sure if there's an equivalent on windows.

Inconsistent file copying speeds across USB devices.

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