Nelson's log

disk speed

2TB USB drives are now under $100. Which is awesome! But boy that’s a lot of disk to write. How long does it take?

Sadly my iMac is USB 2.0 only. In practice that gets about 21 MBytes/second with the disk. At that speed it takes about 27 hours to read or write all 2TB.

My Linux box has USB3 ports, so the data interface is no longer the limiting factor. In practice I’m getting about 110 MBytes/second, at least at the start of the disk. That’s 5 hours and is presumably gated by how fast the bits are spinning by the read head. Update: took nearly 7 hours, aggregate speed was about 82 MB/s.

(Side note:  how do you know you have a USB 3 connection? The plastic inside the port is colored blue, that’s the first tip-off. On Linux you can also inspect the interface speed with “lsusb -t”; 5000M means USB 3. Details on Stack Exchange.)

I’m not finding a reliable source for theoretical throughput on a 5400 RPM spinning platter. Numbers I’ve seen are in the realm of 50–150 MBytes/second. I’d forgotten it depends on the density of the disk. The little 2.5″ disks I prefer should be faster than bigger 3.5″ disks, all things being equal.

There are a few 7200 RPM 2.5″ portable drives out there now, but they’re unusual enough that they are expensive and I don’t fully trust them. Naively, at best that’s a 33% speedup for bulk throughput, not a huge difference. Faster seek times though.