I have 4 external HDDs that I want to keep connected to my desktop. It is likely that more than one of these may be turned on and in use at the same time. All of these HDDs are USB 2.0 and my desktop has built in USB 2.0.
1. Am I correct in assuming that with more than one HDD turned on and connected (but not actively transferring data) the theoretical USB 2.0 bandwidth limit of 60Mbps will still be mostly available to the one actively transferring HDD?
2. If more than one HDD were to be actively transferring data, then am I correct in assuming that each of the active disks will be limited to the total bandwidth divided by the number of active disks? That is to say, if I have 2 of the disks actively transferring data, then I can get a theoretical maximum of 30Mbps from any one of those active disks.
3. If so, then would I see a better overall & individual performance if I use a USB 3.0 hub connected to my desktop via a USB 3.0 PCI card? My assumption being that the larger bandwidth of USB 3.0 will be split between the active HDDs, which (even in the worst case of all 4 HDDs actively transferring) will still be better than the total USB 2.0 bandwidth.
If you're comparing the USB HDDs plugged directly into your computer via USB 2.0 vs using a USB 3.0 hub, I would imagine you may or may not have the first 2 problems. If you are talking about a USB 2.0 hub vs. a USB 3.0 hub, then that assessment should be accurate (aside from your numbers). I would imagine that it's probably better to use the USB 3.0 hub, plus it gives you an easier upgrade to USB 3.0 external hard drives (waaaay better than USB 2.0 ones).
I would go with a USB 3.0 hub vs a USB 2.0 hub. BUT if you are plugging each hard drive directly into its own USB 2.0 port, dont use the USB 3.0 hub, just keep them plugged in to their own port (unless you need those ports for something else, than use the USB 3.0 hub).
But i dont think you will notice any difference between a USB 3.0 hub and a USB 2.0 hub. the only reason to go with a USB 3.0 hub is to prepare for those eventual USB 3.0 externals
on the contrary, if you are transferring data from 2 hard drives (i.e. from one to the other) via a hub, a usb 2.0 hub would likely get you somewhere around 15-20MB/s r/w speed for each device (assuming large files that are contiguous on disk). If you did this same procedure on a usb 3.0 hub, you would likely get somewhere around 30-40MB/s for each device. Note the fact that the latter will take 1/2 the time, an easy difference to tell if you're transferring GBs of data. If you replaced each of those drives with a USB 3.0 one down the line, you'd likely double that number again. USB 2.0 isn't enough for a single HDD, let alone 2; USB 3.0 can easily handle several HDDs at once.
Just wanted to add a few more details. I will need to use a Hub, as I am running out of USB ports on the computer and I also need to "distance" the HDDs away from the computer (and using a Hub with a single cord to the PC, will work better than having 4 cords running back to the PC). Additionally, the HDDs will be will be for - 1 x backup, 2 x media, 1 x docs & pictures. Except for the media, the likelihood of the other HDDs having to transfer large files is low.
In case of media, there will likely be 2 specific use-cases - play media from disk and store media to disk. The Play media use-case is the one that I am most "concerned" about as I dont want the bandwidth to become a bottleneck in playback for large, high bandwidth media like blu-ray dumps. All the other use-cases are not time-critical, though I would still like to get the best performance to cost ratio.
If USB 3.0 is not required at this time, then I will wait for the prices to come down to commodity levels before switching over. On the other hand if I do purchase any new external HDDs, then I will consider buying a USB3.0 enabled (or maybe an eSATA enabled) HDD - to be future compatible.
It looks like USB 3.0 hubs (supporting 4 ports) are in the range of $27-40.
If you don't think you'll be moving files around very much, then a usb 2.0 hub will probably suffice. I'm pretty sure USB 2.0 should be able to handle the toughest blu ray dumps you can throw at it as long as it's defragmented reasonably. Where USB 3.0 helps is only really if you are looking to add USB 3 HDDs in the future or if you find yourself moving media between multiple drives w/ some degree of frequency. If either of those two meet what you expect, then go for the USB 3 route, otherwise save a few bucks and go USB 2