HDD's attached to USB hub

[quartzz1]

Not quite sure where to put this.. anyway

Laptop (with USB 2.0 ports) with a USB 3 hub connected to it, and 2x 2.5" Sata hard drives connected to the hub (using Sata to USB adapters)

If I copy data between those hard drives, does the data go directly between them? or would the data travel back up to the USB port on the laptop, and go via......some motherboard electronics?

I've actually just done a copy, the data rate I got was about 17MB/s (140Mb/s). which seems on the low side, but...not too bad

 

[mikeymikec]

The drives will get USB 2.0 bandwidth, if that. A USB hub is little more than a '3 in 1' adapter, it's not a host controller.

These aren't USB-powered drives, are they? Is the USB hub also USB-powered? If so, I'd almost completely guarantee that they will power cycle due to not enough USB power until one or both drives die.

 

[quartzz1]

thanks so the data would go via the motherboard? hub is self powered, 3A rating I think

 

[mikeymikec]

thanks so the data would go via the motherboard?

I'm straying out of my comfort zone here in terms of confidence. I assume that USB data transfers work just the same way as SATA transfers so they take advantage of features such as DMA so therefore the CPU doesn't have to handle everything from start to finish, so they still go through system RAM before reaching their destination.

What I am pretty certain of though is that when data is retrieved from a storage device, it has to go through its host controller in any case, so your USB 2.0 board comes into play there.

Do you have the option of sticking a USB 3.0 card into your computer?

Also, if you can bypass the hub completely, I would if I were you. Two USB-powered drives will consume a lot of power. How much depends on the drives / their enclosures.

 

[mindless1]

Yes, the data goes through the USB3 hub, to the USB2 controller in the laptop, into main system memory, then back out the way it came.

17MB/s seems about right, around half of the typical max you could expect over USB2, divided by 2 because you have two drives on the same controller.

There is no practical way around this on an old laptop, unless you have an optical drive SATA port with a standard SATA connector that you can use for one of the HDD, then you would get closer to 34MB/s over a single drive on the USB2 port.

It seems rather fiddly, if performance is important it is time to think about getting a newer laptop with USB3, and SSDs wouldn't hurt either, though for large writes a modern USB3 flash drive isn't too shabby as long as it's not one of the tiny ones that gets hot and throttles down performance.

 

[quartzz1]

cheers. tbh, it's a once-every-few-weeks backup, so the data rate isn't absolutely critical. it is a moderately old laptop (Fujitsu lifebook A531, i5-2450 cpu), with an SSD installed into it. the laptop is still going fairly strong, with the exception of some strange occasional interference lines appearing on the ViewSonic monitor I have plugged into the HDMI.....but that could be another post

 

[VirtualLarry]

Does that laptop have an ethernet port? If so, consider using a NAS to backup instead. A 1GbE port can handle 110MB/sec transfers.

 

[quartzz1]

it does have ethernet, tbh, the usb hub is a temporary arrangement, eventually the 2.5" hdd's will be going into another desktop, Wifi'd to the router. the backups will eventually be 2x sata drives connected directly to a micro atx mbd. eventually. possibly 😛. can you get a network attached storage device, that consists of 2.5" sata slots? (or possibly 3.5"s with an adapter) and importantly, can you password protect a NAS?

 

[mindless1]

You could put 2.5" SATA HDDs on an adapter for 3.5" HDD rails, but do you really need 24/7 access, networked, that needs password protected? That seems like additional (unnecessary) risk and wear on hardware for something you do "once-every-few-weeks".

I would just get $15/128GB, $30/256GB, etc flash drives, if you don't already have a NAS or desktop over GbE, but yes you can password protect it.

 

[Paperdoc]

A couple comments.

RE: data flow in this scenario. The USB system does not make fancy use of mobo connections between semi-intelligent device controllers, because it is not restricted to particular HDD units. It is a VERY general interface for I/O devices. So all data wil travel through the USB2 system into the mobo USB2 controller and thence through the CPU (andl likely RAM used for a buffer) and then back out the same path but to a different end device (the second drive). mindless1 is exactly right that this means the net data transfer rate should be about 1/2 the max rate of a USB2 system.

Putting your backups on an in-house network storage unit does not really fit the ideal backup system. Your backup medium should be something that you can DSIconnect from all external connections, both for security against external users and for protection from environmental events such as power surges. Further, ideally you should be storing that in a different site to avoid the possibility that the original AND the backup data sets could be destroyed by the same disaster, like a house fire. I recall a large local manufacturing facility that had its data centre in the basement floor of the main office building. (I know, bad planning from the days when data handling was one of those lesser tasks delegated to Accounting.) Anyway, there came a flood and the entire area was under several feet of water. A good time NOT to have your backups on-site! As an extremenly rare counter-example (maybe), there was a story that, in the 9/11 disaster, one company lost all its data AND backups because the backups were stored in the OTHER twin tower.