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A colleague told me that it is not recommended to use USB hard disks due to the lack of inherent integrity checking of copied files. I am looking for details on that. In what respect is copying to a USB device different from copying to a hard disk connected via e.g. SATA? If anybody has further sources/information on that, I would appreciate sharing it with me.

edit: As explained below, I know that in many cases, the used hard disk is effectively nothing else but a SATA disk in a casing. My question is whether the USB <=> SATA interface introduces data security issues. My colleague referred to a case where a broken USB controller led to data loss. Data could be copied to the hard disk without any problems, but the data written to the disk was corrupted. Replacement of the USB controller resolved the issue in this case.

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    They often are the exact same HDDs I assure you the firmware does the same integrity checking if you removed it from the enclosure and attached it directly to your SATA bus.
    – Ramhound
    Commented Sep 17, 2014 at 10:26
  • @tamy - Yes, broken hardware can produce weird and unfortunate effects. That's why a lot of backup software goes back and re-reads what it's written to make sure it's really there. This (rather unusual) failure is reason to get new backup software, but not to discount USB hard disks.
    – Michael Kohne
    Commented Sep 17, 2014 at 12:03
  • @Michael: So you would assume the USB interface is vulnerable to such issues to the same extent SATA is?
    – tamy
    Commented Sep 17, 2014 at 12:20
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    @tamy - EVERY interface is vulnerable to some issues. NOTHING is perfect. You could get a defective drive. You could have a solar flare while doing backups. If the backups are that important, you need to CHECK them by reading after writing. Your co-worker is getting worked up about one unusual failure he saw once upon a time, and potentially ignoring other problems and the appropriate way to deal with them. You have to evaluate a proposed backup system in total, INCLUDING what happens when hardware fails.
    – Michael Kohne
    Commented Sep 17, 2014 at 12:24
  • @tamy - Where does Michael say that? All he said was broken hardware can produce weird results which cannot be predicted.
    – Ramhound
    Commented Sep 17, 2014 at 12:37

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I suppose this could happen, but then again your RAID controller within your server could fail, or the Fiber Channel card that runs to your tape drive, or your tape drive itself could go bad. A consumer USB drive obviously isn't going to be as technically robust as enterprise level hardware, but if your short on funds it's better than nothing. I'd be more worried about the drive itself failing before I'd ever worry about the USB controller going out.

While I wouldn't recommend using USB disks permanently, for a short term backup solution they're fine and the price is right. The biggest downside is their speed, large files take forever.

USB disks + robocopy = low cost backups for many small businesses

I should also state, robocopy verifies the files it copies via checksum on the fly, so if things were to get scrambled on the way to the external drive, it would alert you

And to clarify, I am not saying anyone should avoid USB backups. They are a easy and cheap solution for backups as long as the data stays under 2TB. Go beyond that and backups take too long, and you'll hit your next backup cycle before the last one has a chance to finish.

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  • The author is talking about HDDs connected over the USB bus. Which makes me wonder what your talking about considering (most) of those drives the author is talking about are the exact same drives that are mounted and connected over SATA. In reality the SATA drive is connected to a SATA to USB controller.
    – Ramhound
    Commented Sep 17, 2014 at 12:38
  • I'm talking about the USB controller that the external drive plugs into. I didn't say anything about the drives being different, or being connected to the SATA bus. Drive > USB/SATA interface > USB port
    – Lee Harrison
    Commented Sep 17, 2014 at 12:41
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    I guess I am confused by the reason you wouldn't recommend USB disk as a permanent backup solution. I could list several advantages to having what is basically an offline backup because of a USB HDD enclosure.
    – Ramhound
    Commented Sep 17, 2014 at 12:43
  • I suppose the context I work in (medium enterprise) makes me shy away from USB as a primary backup. I know plenty of SBs that use it, and it works perfectly fine for them. And the cost/offline nature are certainly upsides. The speed is the major drawback though. USB backups become cumbersome once data reaches a certain threshold, I'd say around 2TB. But I'm certainly not saying they shouldn't be used, just use them until you can afford/justify something better.
    – Lee Harrison
    Commented Sep 17, 2014 at 16:11
  • I would agree. After 2TB you can run into performance problems connected to the bandwidth provided even by USB 3. One major problem is you run into performance problems connected to the bandwidth of both SATA 3 and USB 3, both are reaching their limits, to what an acceptable amount of time is to backup 3+ TB of data.
    – Ramhound
    Commented Sep 17, 2014 at 16:17
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One thing to keep in mind is that very few USB controllers pass SMART diagnostic data from the drive back to the operating system. If you had a drive that was close to failure within your USB connected enclosure there is probably no way you would know about until it had completely failed.

There are certain values exposed via SMART that can potentially predict that a failure will happen in the future.

When a drive is connected via SATA/SAS the OS can query the SMART fails and see if there are a growing number of failed blocks or something. On linux it is common to install smartmontools, which will periodically check that all the connected drives are healthy. There are similar tools under Windows.

I would not worry about the chance of a failure of the USB controller at all, that seems very unlikely. The failure of the USB connected drives is far more common.

That said, at both work and home I use USB drives for one copy of my backups. Because I am a extremely paranoid guy, I have two separate backups. One goes to a cloud host, and the other goes to USB connected disks. In the remote chance my USB disk or controller fails I still have a my other backup system. The convenience of USB connections and drives leads me to use them even if their is a remote chance they will fail unexpectedly.

The USB enclosure I use at work will actually monitor the SMART status and indicates a potentially failing drive on a LCD panel. So if you pay enough you can get hardware that mitigates the lack of SMART support via the USB storage protocol.

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Never faced the problem described by your friend. Most of external USB HDD are just SATA drives in case enclosure with integrated SATA to USB adapter. Some of them, however, don't have SATA interface and have USB controller on print board instead of SATA one. In that case, because of it's rarity, it can be harder to repair physically broken HDD. Anyway, I don't see any problems about using external hdd for longterm backups.

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  • This does not address the original question which specifically looks at inherent integrity checking.
    – Matthew Williams
    Commented Sep 17, 2014 at 11:04
  • The problem as I understood it is that (as was claimed) the USB interface in between is vunerable to data corruption...
    – tamy
    Commented Sep 17, 2014 at 11:17
  • @tamy - You information is not valid.
    – Ramhound
    Commented Sep 17, 2014 at 12:39

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