This question makes me reconsider Drobo, but I have a concern about data transfer rates. Wouldn't the USB (or LAN) connection be a significant bottleneck to my system?

My home media center PC has a system disk and 2 x 1TB data disks for video and audio = 3 SATA drives on the motherboard controller. It's a hassle to expand this storage, but perhaps a NAS could help.

If this were on a Drobo, and I use USB to connect it, wouldn't I have much slower data rates? Or if I had a Drobo with LAN, then my LAN would be the bottleneck, right?

I realize a Drobo or any other NAS solution just covers storage, not backup, so ideally one would have another NAS (if I win the lottery) at a friend's place and mirror the two.


If you're connecting over gigabit ethenet and you don't have super-fast HDDs, LAN will not be the bottleneck. USB, however, could be a serious bottleneck. Rough estimation of speeds:

Item                 Bytes/s      Bits/s
----                 -------    --------
USB 2.0:              60MB/s     480Mb/s
7200RPM HDD:          70MB/s     560Mb/s    (average hard-drive)
10000RPM HDD:        100MB/s     800Mb/s
Gigabit Ethernet:    125MB/s    1000Mb/s
2x 7200RPM RAID0:    300MB/s    2400Mb/s
FireWire 800:        400MB/s    3200Mb/s

1 Byte = 8 Bits

  • By this chart, it would be smartest to use Firewire if present. – Torben Gundtofte-Bruun Aug 18 '10 at 14:18
  • It kind of depends what you're doing. If you were backing up information from your hard disk to this FireWire 800 device, your transfer speed is going to be that of your slowest component. You can't write data to the FireWire 800 device faster than you can read data from your hard drive. – JBirch Aug 18 '10 at 14:32

You would definitely get lower speeds over USB, with a Drobo or anything else. All the drive's I've attached via a USB2 port top out at a little over 25Mbyte/sec for bulk operations - much slower than your internal drive controller will manage and with a CPU hit due to the design of the USB protocols too.

If your LAN is gigabit then you should see better rates than USB for bulk operations - about 50Mbyte/sec is the best I've seen between machines over gbit ethernet, though I've not tested this extensively or at all scientifically. This will still be slower than internal drives under ideal circumstances (bulk reading with few head moves) though for random access the difference will be less (once the drive heads start needing to move around a lot their latency will become the bottleneck not the throughput bandwidth available between the controller and the PC.

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