I've been reading about backup solutions and have come across a number of people saying they use a USB external hard drive as part or all of their backup solution.

Are USB hard drives really sufficiently reliable to use for backups? From what I read in the past (e.g., Why I'm done with portable hard drives | Computerworld Blogs) they are rather failure-prone, especially apparently USB-only ones where the USB controller electronics have a high failure rate. Personally, I've only ever had one, a mid-price Western Digital, which has had some issues and I stopped using.

I understand there are some factors that substantially affect reliability, which AFAIK are whether the drive is moved much, whether it has its own power supply, and whether it has adequate cooling. Perhaps the drives are more reliable now than they used to be? Perhaps if they last through an break-in initial period they then tend to be reliable?

  • you can also backup to a place like crashplan, and you can set your own encryption key. – cybernard May 14 '18 at 3:15

"...part or all of their backup solution."

USB HDDs for part of the solution is okay. For all of the solution, it's not a good idea.

When you plug in your USB HDD, your entire backup medium is now online and writable, on the same machine which has your primary data.

In the event of:

  • a glitch in your backup software
  • an electrical failure
  • a virus
  • human error
  • fire or flood

You could lose all your data, even your backups.

One poor-man's solution would be to use two HDDs, keeping one off-site and off line (e.g., at a friend's house).

The disks are reliable. Some USB electronics are flaky, so test your backups.

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    Great answer. I'd add that using an external USB enclosure which can be disassembled easily and hard disk removed, allows you to recover data in case USB enclosure electronics fail, but the hard disk inside is ok. – haimg Dec 13 '11 at 18:34
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    +1 Also, backing up to a USB is going to be slow, especially over USB 2.0. eSATA may be a better choice for external drives. – Andrew Lambert Dec 13 '11 at 18:39
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    I was hoping for real data on the reliability of USB drives, but I suppose that isn't the precise question I asked, plus I'm starting to wonder whether such data really exists. Still, if someone has that, I'd be happy to give them credit instead of I can. – Paul Dec 14 '11 at 19:06
  • There is a huge array of USB drives, so answering that question in general is very hard. You can look up reliability for most individual drives, especially the upper end ones, on the manufactures websites. Also, it will matter to a degree how much you move/toss it around. As a general rule, they are reliable enough that its not an issue for an average end user, but no existing medium is so reliable as to be trusted for a sole backup. – TimothyAWiseman Dec 14 '11 at 22:41
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    @Paul, They're the same HDDs inside your computer. Aside from being carried around and bumped and stuff, there's no difference. The USB-SATA adapter and the external power supply are your most likely electrical problems. There are a lot of cheap manufacturers with weird names who produce bad enclosures, but in my experience, when they fail, they fail the first time you try to move a few gig back and forth or leave them on for a few hours... buy from a good computer store with a good exchange policy and test some heavy transfers before you rely on an enclosure. – mgjk Dec 16 '11 at 14:21

I have been monitoring backups to USB drives for three years after I noticed too many failures with client's drives. Monitoring the event log on the computer being backed up has been revealing. Even with backups that are successful, write errors are recorded in the event log. Subsequent disk checks of the USB drives revealed either bitmap errors or MBR errors. Since any disk error will eventually lead to data corruption, it is a disaster waiting to happen. Even though the backup may be "successful" according to the backup program, write errors or disk errors count as a failure as you are playing russian roulette with your data. As Journeyman said, the point of backing up is to not have failures. Backing up a 99.999% reliable device with a 90% reliability device does not make sense. So I have opted for backup to NAS onsite and offsite backup through the internet.

The reasons for a high USB failure rate are actually quite simple, but not always possible to avoid.

  1. Failure to remove drive through "Safely Remove Hardware" icon.

  2. A full computer backup through software such as "Shadow Protect" (my favourite) push through large amounts of data at high speed. While most USB drives are sold with high data rates, the reality is that sustained high data rates create heat in the USB electronics. And since most USB drives do not have fan cooling, the electronics go over temp and stop until they cool down. Some drives are better but they all do it.

  3. Again because of high data rates and no fan cooling the actual hard drives quickly go over the rated internal temperature, the temperature of which varies from drive to drive. And the higher the temperature the quicker the rate of temp rise. Hard drive life is shortened but an instant killer is immediately unplugging the drive while it is still hot.

  4. The way people handle or abuse USB drives causes pre-mature failure.

  5. The failure of some USB drives to properly dismount, so the client unplugs it anyway.

I have had to recover data from countless USB drives for clients, and the failure rate is too high. Several times, when client computers bit the dust, a restore from a backup USB drive also failed.

As per Ligos, taking the drive out of the USB case will help but this is not a commercial solution. Some drives still get piping hot even out of the case, and forced air cooling is necessary to get the drive under max rated temperature. I use HDSentinel to monitor temperature and also for general drive health checks.

There use to be small Verbatim portable drives that had a fan and connected by Ethernet but they are no longer available. For the moment it is backup to NAS and online backup for critical data.

  • Thank you Samuel. That's extremely helpful, and just the sort of additional data I was looking for. Pity I can't mark two items as the answer to the question, but I did at least upvote it. – Paul Oct 22 '13 at 20:14

I've had 2 USB HDD's fail on me in the past. Both due to HDD failure (the USB enclosure is still working; verified by plugging the HDD into another computer).

100% of my failures have been due to accidently dropping the drive, having it fall off a table, having the cable wrenched out at unexpected times, etc. Basically, my own negligence and stupidity.

I fixed this problem by taking the HDD out of the USB enclosure and connecting it via the internal SATA interface in my home media PC. There have been zero failures over an equal period of time since I took me out of the equation!

Remote backups are done via a remote backup service over the Internet.


The point of backing up is not to not have failures. Its to not have a failure when you have another failure going on at the same time, and the thing that failed is needed to fix something else thats failed.

Nothing is failure proof, you're playing with failure curves. Internal drives fail, external drives fail, every so often entire BUILDINGS AND INFRASTRUCTURES fail.

So, yes they are. Just don't entirely trust the sneaky buggers and have enough backup backups to sleep well at night ;p


I agree with mgjk but to expand on it a little, USB harddrives are relatively reliable. I have had some last for several years. I have had some fail on me, but then that is true of the primary harddrive inside the computer too.

Any harddrive, indeed any storage medium at all, will have a failure rate. That is why for files that are truly valuable you should have redundant backups, no one solution will be perfectly reliable.

At home I backup my files automatically to my NAS as well as using dropbox for many of my key files (in conjunction with truecrypt for the sensitive ones.) I also occassionally burn a DVD with the files that I know I want to archive for the long term. I would not fully trust any single one of those solutions, but together I know the odds of them all failing at once are acceptably low.

  • Thanks, your data is very helpful. I've actually been very fortunate with internal drives, perhaps because I tend to replace them after a couple of years. – Paul Dec 14 '11 at 19:09
  • Yeah, I tend to keep upgradin computers rather than replacing wholesale, so I have harddrives die on me from time to time. – TimothyAWiseman Dec 14 '11 at 22:37

The failure rate of external USB drives can not be compared to internal drives. USB drives fail all the time. You can not expect them to last. They will fail.

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    Why? Their mechanics should be an ordinary laptop drive. – peterh Feb 29 '20 at 11:17

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