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I know the theoretical maximum transfer speed of USB 2.0 is 480mbps, which calculates to be 60 MB/s. If I have 10 external hard drives in RAID0 all plugged into 10 USB ports at the same time, will I still not be able to get any faster than 60 MB/s?
usb_raider
Posted 2011-12-20T04:00:59.133
Reputation: 11
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Yes, and no. The combine throughput of 10 computers with one USB 2.0 harddrive each would be 600MB/s (theoretical). The problem with having all those harddrives on one system is that you start to hit other bottlenecks in the system.
We're working with a combined bandwidth of over 4 Gbps, and each USB controller can only handle 480Mbps. You would need to use 10 host controllers, one per harddisk, to have that much USB bandwidth in a single system. You would also need to make sure that the southbridge or wherever the controllers are connected to the rest of the system can also handle that much bandwidth. If you put 10 pci-e expansion cards in a single system, theoretically you could reach those speeds. Good luck finding a motherboard with 10 pci-e slots.
Darth Android
Posted 2011-12-20T04:00:59.133
Reputation: 35 133
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Most modern motherboards at least have separable USB lines for its front hub and back hub. So if you plug in some hard devices into the front panel and some to the back, you should be able to get over 60 MB/s limit.
user1032613
Posted 2011-12-20T04:00:59.133
Reputation: 296
Its not going to be possible to transfer faster then the 60MB/sec limit. What you describe about the front and back hubs are true, your statement about going over the limit, is just plain wrong. Besides I don't even know if its possible to setup a RAID on external devices like this, I would be shocked, if a software raid would let this happen. – Ramhound – 2011-12-20T19:18:04.100
No reason a softraid should explicitly disallow this if such a setup is, in fact, what the user wants. MDADM in linux wouldn't have an issue with it to my knowledge. – Darth Android – 2011-12-20T19:33:55.820
@Ramhound, sorry I'm confused, but please explain why my statement about going over the limit is "just plain wrong". Also, as said by Darth Android, I've made a RAID0 with 4 removable disks with mdadm command just fine. – user1032613 – 2011-12-20T21:58:13.483
I'm pretty sure the 480 mbps is per USB bus. Each bus has one host controller. Thus 480mbps is per controller. So no matter how many devices you plug into one controller, the bandswidth is 480mbps. – surfasb – 2011-12-20T09:28:01.630
1Thanks. I was pretty sure, but not completely sure, hence the ambiguity. I've clarified to indicate that you'd need 10 host controllers. – Darth Android – 2011-12-20T15:44:41.167
Then again, I'm not 100 percent sure either. I came to that conclusion based on two things: A usb device can choose from certain kinds of connections that may or may not guarantee bandwidth and all connections in the USB is initiated by the host controller. We'll need someone nerdier like grawity or Moab :) – surfasb – 2011-12-20T17:41:50.280