I am considering purchasing one of the following for data backup purposes. In either case, they would be used with a USB 2 port on XP Home SP 3.

Is there likely to be much speed difference when reading/writing files from/to these devices? If so, to what effect is there a speed difference? For example, if I want to read/write 5GB of data from/to these devices, would the HDD be much faster than the flash drive?

  • one's bigger ;) – Journeyman Geek Aug 7 '11 at 11:42
  • First link in question now gives a 404 error, due to a recent edit. – Goto10 Aug 10 '11 at 20:56

Yes, there will be a difference.

As far as I am aware the faster USB flash drives tend to be around 20MB/s write speed (but speed varies a lot depending on manufacturer and controller) while hard drives tend to pretty much saturate the USB port and transfer near the limit at around 40-50MB/s

Hard drives are much faster at bulk data transfers, while Flash devices tend to be much faster at finding small bits of data quickly.


To answer your comment

You can get some portable 500GB drives that will work from USB bus power alone, they tend to be based on laptop hard drives and can be a bit slower than the full size hard drives, but generally they're fine. An example is this one.

A full format can take quite a while and it only takes longer the larger the drive is, with an approximate 500GB drive I would expect a full format to be of the order of 3 hours at USB speeds

(500*1024)Mbytes / 40MBytes/s =  12800 seconds
                              = 213 minutes
                              = 3.5 hours (approx)

It may end up being a bit faster (something like 2.5 hours) due to getting slightly better speeds (USB can theoretically get up to 60MB/sec, but there are protocol overheads and other devices that share that speed), manufacturer megabytes (as manufacturers do not measure a megabyte the same way everyone else does) and other factors. Heck, it may even take longer if it's a particularly slow drive or the USB bus is doing other things....

Generally though, USB drives come preformatted, have protection (S.M.A.R.T.) so that if they fail to write a sector they will remap the sector out of the usable portion of the drive, and a quick format will suffice 99% of the time.

  • The specification for the above flash drive says - "Write speed: minimum 3MB/s (20x)". – Goto10 Aug 7 '11 at 16:29
  • Then if you even vaguely care about backing up large files quickly I would go for the hard drive, if you want portability then the flash drive... As I should have mentioned the "faster" flash drives are ones you pay for the extra speed. Hard drives tend to be bulkier but both faster and with a heck of a lot more storage space. – Mokubai Aug 7 '11 at 20:07
  • Just wondered - how long roughly does a 500GB portable HDD take to format (using a full format)? Also, will there be sufficient power for a HDD to work from just one USB port (if not would two be enough?)? – Goto10 Aug 10 '11 at 11:08

For backup, I will go with HDD. It's less expensive per MB and faster.


Anandtech just tested a USB 3.0 USB flash drive. They can be quite a lot of faster than a hard disk drive if the interface is fast enough, like USB 3.0 or eSATA.

However, the price with the fast models is high, around $2 per gigabyte and reliability of USB flash drives is often worse than hard disk drives. On SSDs the unreliability is compensated by installing more flash memory chips than is actually used at once, and moving blocks out from bad blocks on the fly. However, in a lot of cheaper and smaller flash storage, USB drives, measures like this are not usually done.

So, for backups I'd go with hard drive, and if you can, use eSATA or USB 3.0.


I conducted some tests. Here are the results... [one 3GB file copied]

  • 1TB or 2TB USB 3.0 Toshiba external hard drive (portable HDD with 5400 RPM drive) connected to a USB 2 port of a laptop ~ 110 MB/sec

  • 16 GB USB 3.0 flash drive (SanDisk Ultra Fit thumb drive) connected to a USB 2 port of a laptop ~ 11-14 MB/sec. Performance tested by other manufacturers were similar (11-17 MB/sec)

  • 16 GB USB 2.0 flash drive (thumb drive) connected to a USB 2 port of a laptop ~ 3-4 MB/sec

Please note that copying many smaller files will show different performance.

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