Ten external hard drives through a USB hub

Question

I have bought a 10 port USB Hub with power, and attached that to one port at the back of my PC. Connected to the hub are ten external hard drives.

Is this set-up safe, or can it do damage to my motherboard?

Solution

It's safe. I'd give you a more detailed answer, but I don't know what hazard you're imagining, so it's hard to know what else to say.

Comments

[Karan]

Ok, I have a follow-up question if you don't mind. :) Even if it's safe (and yes, I know it is), surely at some point it becomes impractical to tack on more devices that are simultaneously transmitting/receiving data, because the port/controller's bandwidth gets exceeded?

[David Schwartz]

It depends on whether you want to access many of the devices at the same time. If you're only going to access one or two devices at a time, then it doesn't become impractical -- even to add a hundred devices.

[MSalters]

That depends on the harddisks too. If those have external power, they won't draw power through the hub.

[user5249203]

To elaborate a little on MSalters comment: You can quantify "a lot of power". USB 2.0 allows for up to 500 mA per port, so 10 ports could draw no more than 5 Amps. In practice, unless you are using bus-powered 2.5" HDDs, the disks would have their own power supplies and the hub would need to supply negligible power and so might easily operate using only the <500mA it can draw from the PC.

[Karan]

Yep, that's why I said "simultaneously".

[David Schwartz]

@Karan: I would say no, it doesn't become impractical. No matter how many devices you have, the bandwidth available is the same. It doesn't follow that more devices require more bandwidth, even if used at the same time. (For example, if you're trying to write 40MB/s, it doesn't matter if you're writing it to a 3 disk RAID 5 array or a 32-disk RAID 5 array, the bandwidth required is essentially the same.)

[Karan]

Yes, but that's the same data being written. What I was thinking of was separate devices transmitting/receiving their own data simultaneously via a single USB port. Surely there should be some bandwidth limits there and using too many apps together might saturate the connection?

[David Schwartz]

Sure, but that's independent of the number of devices and solely dependent on the amount of data you have to move. Adding more devices in no way reduces the amount of data you can move. How much data you have to move depends on how much work you have to do, not how many devices that data has to go to or come from. If adding more devices means adding more work that has to be done, then it will take longer to accomplish the greater amount of work.

[Scott Chamberlain]

Just to clarify, and @DavidSchwartz correct me if I am wrong, David is saying you should not be comparing 10 GB to each of 10 drives (each getting different data) compared to 10GB to 1 drive. What you need to compare is 10 GB to each of 10 drives (each getting different data) to 100GB to one drive. Because you need the total data transfered to be the same for both cases.

[TFM]

Why not give us the "more detailed answer", so others can benefit from it as well? Or should we just take your word for it?

[David Schwartz]

@TFM: Because the question is unbounded. You can't really show that something is safe, you can only refute arguments that is has specific risks.

[TFM]

@DavidSchwartz: I have higher expectations from a technical community when it comes to answering questions of this sort. It's worse to give accurate answers like "It's safe" when a question is unbounded, because you don't know all the circumstances around how the OP will use his/her 10 drives.

[David Schwartz]

@TFM: It is almost impossible to give a great answer to a poor question. Your expectations are not realistic.

[TFM]

@DavidSchwartz: "It is almost impossible to give a great answer to a poor question". Well, then, you don't have to answer it. Just keep your finger off the return key.

[Loren Pechtel]

I don't believe there is a 10-port hub out there that can provide what the spec says the ports must. My 10-port has a powerpack that is only rated for 2.5 amps--it would have to be 5 amps just to power the ports with nothing left over for the hub electronics.

[MSalters]

@LorenPechtel: I'll bet that's 2.5 amps at 12 volts (30Watt). 10 USB ports at .5 A/5V would take only 25 Watt, leaving 5 Watt for the hub itself (entirely reasonable, even ignoring the fact that it can draw another 2.5 Watt from its upstream connection)

[Loren Pechtel]

@MSalters All the ports must have the same ground point.