USB 2 Speed with an external harddrive?

[Birger]

I?ve just used an external harddrive (Hitachi 7K250) and copied some files too my internal harddrive (also a Hitachi 7K250) and I noticed that I only got a speed of around 18600 Kb/s too 18900 Kb/s and want too know if someone of you could explain to me why I got so low speed?

Since USB 2 should bee capable of 480 mbit/s (60 Mbyte/s) why did I only get a transfer rate of around 155 mbit/s (18.5 Mbyte/s) from an external harddrive?

I?ve got an Abit NF7-2 motherboard.

 

[gaidin123]

I've seen peaks somewhere around 20-25MB/s with an external usb2 hard drive. I can't tell you the exact reason why you don't see the theoretical transfer rates but some probably valid reasons are:
Bus overhead
Drive transfer speeds don't approach 60MB/s
Nothing ever reaches its theoretical bus limitation
USB2 bus is possibly shared on the PCI bus which other devices are using

I wish it was faster too. If you look at AT's recent NF4 Ultra motherboard roundup the tests on external usb2, firewire400, and firewire800 show that if you want the fastest external drive you need to get a sata one. Barring that get a firewire800 card/case. FW800 has a 100MB/s theoretical limit and nothing is getting close to that.

Gaidin

 

[PhlashFoto]

I use an external combo FW400/USB2 drive. Basically, as gaindin pointed out, I to get about ~ 21-25MB/sec trasfer rate on USB2, and around 29MB/sec or so with FireWire400. This is normal for these external drives. To add to gaidin's reasons. I think what else could also lead to the lower performance is that AFAIK, most if not all of the external cases are using PATA drives. (If there is an external SATA case, please someone correct me, i dont keep up on that stuff.) Whereas, FW and USB are both serial interfaces, so there is a bit of performance drop for translation.

Also what I dont like about USB is that it eats up more CPU clock time than FW. So I always tell ppl that FW is much better.

 

[gaidin123]

There are external direct sata cases. It's not really an official standard, that's the new esata stuff but take this one for example:
External SATA case

That case takes a sata drive and puts a sata connector out back. I don't own this (thinking of buying one) but that should provide you with dramatically quicker speeds than external firewire or usb2 drives.

That is a good point about converting between PATA to a serial bus, I hadn't thought of that one.

Gaidin