When should you turn off an external hard disk?

Here's an interesting question: should I turn off my external hard drive when not in use? Leo Notenboom, who I mentioned back in July, addressed this issue a few days ago on his Ask-Leo.com Web site.

In short, there is no one clear answer, a number of issues have to be considered. What surprised me, though, about Leo's answer, was that he didn't mention my reason for turning off my external hard disk.

(Credit: Western Digital)

Being a pessimist is necessary for defensive computing. The main reason I turn off my external hard disk is to protect it from me.

When my computer boots, the first thing it does is run a scheduled backup of my important files to the external hard disk. After I verify the backup ran successfully, I turn off the hard disk and leave it off until the next backup. The disk is used exclusively for backup. My backups are run by a .bat file and, in case I forget, the last thing it does is remind me to turn off the hard disk.

Why? With the disk off, I can't delete files by mistake. And, should some malicious software make its way onto the computer, it can't screw up files it doesn't see. Finally, hard disks run hot (I've seen up to 140 degrees Fahrenheit) and while there are, no doubt, air vents in every enclosure, it's only a matter of time until dust clogs them up. An external hard disk that runs for only a few minutes a day will never get dangerously hot, even if all the air vents are clogged.

But that's me. Read Leo's response and decide for yourself.

I'll contact some hard disk vendors and point them to this posting. If any of them respond with a recommendation I'll let you know.

Update: January 2, 208. I have heard back from Western Digital and Seagate about this. I hope to hear from some other vendors and gather their recommendations together in a couple days.

See a summary of all my Defensive Computing postings.

[lnotenboom]

You raise a fine point.

There are two reasons I leave mine on 24/7: the primary one is simply that I'll forget to turn them back on, and as a result will have NO backups for the duration of my forgetfulness. (My backups are scheduled, and happen in the middle of the night while I sleep.) The second, less important, reason is the whole heat up / cool down issue that I mention in my article.

Hope you do get specific recommendations from manufacturers, I think that'll be very interesting.

Thanks!

Leo

[mhinnewyork]

Leo,

Interesting that both of us came to our decision, different though they may be, for the same reason - we don't trust ourselves. :-)

Michael Horowitz

[john55440]

I was told by a hard drive manufacturer that I should use Safely Remove Hardware before turning off my external hard drive, even if the USB cable stays attached. Were they wrong?

I have been keeping my external hard drive going 24/7, partly because I am too lazy to use Safely Remove Hardware every single time that I want to turn it off.

[john55440]

MH, here is a subject for you to blog about:

Last year, employees of a major computer repair chain were caught viewing/copying customer documents, in violation of the computer repair chain's corporate policy. What are some ways that a computer user can protect financial and other documents from the prying eyes of computer repair people? Do you have a favorite brand of folder-encryption software? Any other ideas?

In addition, if memory serves, the same computer repair chain (at least) once accidentally backed up the documents from one customer's computer, and restored it to another customer's computer. The second customer ended up with all manner of financial and other documents, that weren't his.

[protagonistic]

There are several reasons for leaving both my external and internal drives running 24x7. I do not allow the computer to spin down internal drives when not in use.

Probably more a carry over from the early days of Winchester drives, think early 70's here, is that the time you put the most stress on a drive is when you are starting and stopping it. that along with constantly changing the temperature you expose the circuitry to can be hard on a drive.

My second reason is more a matter of experience. Modern hard drives have a MTBF of many years. I have been in computers for almost 40 years and the people who always seem to be having HD failures are those that are always turning the drives on and off. Those that leave them running have been pretty much trouble free in that department. Anyway, thanks for the chance to comment.

[raininthebrain]

In the IT world, hard drives never turn off. Servers are powered on 24x7. So my thoughts and opinions will be IT oriented. The heat that is generated from your external hard drive seems a little extreme. I run an external Maxtor 500GB connected via USB to my primary office computer and it never gets even remotely warm (excellent cooling). When I wish to backup my data, I use a method similar to a Unix rsync which ensures that all files are copied and doesn't copy files that haven't changed. This is very similar to an incremental/differential backup but can be run in the background within a batch script. Furthermore, what about creating a small file server where you store your important files that require a little more security? All the big name hard drive manufacturers offer some inexpensive NAS based solution which allows Windows to mount via a drive letter. Chain two drives together, RAID1. Now your files are safe with a little added security of mirrored data.

[tehrani625]

I was wondering how you would do a raid 1 with a pair of WD mybook pro drives 320gig conected via usb?

[g-mat]

I heard somewhere that turning the hard drive on and offwhile the computer is running could create a risk of data corruption. Since I usually leave my desktop running I usually don't turn my hard drive off. Have I completely misinterpreted something?

[mhinnewyork]

Two of these comments made me realize that both Leo and I left out something that is obvious to techies, but may not be to everyone. Before powering down an external hard disk you should logically disconnect it.

In the Windows world, this means using the "Safely remove hardware" icon in the system tray (a.k.a. notification area). Its the icon with the green arrow and a gray blob underneath the arrow. Click on the icon once and it will show you all the drive letters than can be logically disconnected. Just select the one in question. Sorry about the omission.

If any Mac or Linux users know if this is true in your favorite OS, please leave a comment here. Thanks.

Michael Horowitz

[ruminator]

So for the non-geeks could you elucidate on your other omission--viz., why you need to "logically" (do you mean physically) disconnect the HD before powering down or shutting off?

[Taylor McLaren]

Mac OS (or 10.4, anyway) shows external drives right under internal and/or bootable drives in the Finder sidebar, and there's a little eject button next to each one, just like CDs. Not only do you have the option of dismounting drives before disconnecting them, but the OS tells you off -- some message about possible data corruption -- if you don't.

[peripo]

thanks for this, I never connected the "Safely Remove Hardware" icon with unloading a hard drive - thick thick thick - despite moving to Mac last year, I still have a couple of PCs I turn on occasionally.

With OS X, just right click over the drive you want to disconnect and select "Eject". If you don't eject it before unplugging, it puts up a petulant little message about damaging your data. I always feel like I've been 'told off' by the teacher and make sure I always Eject before I disconnect now.

[FrankTurd]

>>And, should some malicious software make its way
>>onto the computer, it can't screw up files it doesn't see.

See, this is an excellent reason. I turn my external off for this very reason also as my external is used primarily for back-ups as well small, nefarious bits-and-bobs. That last issue I want is to deal with is malicious software that cleans me out totally with zero back-up.

[WildSignals]

I've been using an enclosure for years on an external USB connection. I hook it up to a power block along with my desk lights. So I know it'll only be on when I am sitting there and turn the desk lamps on.

A USB connected drive in Windows XP or Vista, won't have "Write Cache" enabled. Meaning it won't cache something that needs to be written to the drive in RAM and write it later (you're normal hard drives do this, but not USB connected). This makes the drive somewhat slower than a standard hard drive, plus USB 2.0 is slower. However, it also means that unless you have a file open on the external drive, you should be able to turn it off without issue.

Safest thing: Log out of Windows first, then shut off your drive. Then you know all file handles are closed. Doing that, I've never had a problem powering it off with my desk lights.

[alias2]

I have a macbook pro. I disconnect them when finished with computer to protect them from myself and electrical surges.
Once I had left it on and came home, the electricity went out and computer told me disconnect error. Thank goodness nothing was missing or corrupted.
Another time I accidentally pulled the cable out when moved laptop.
I always disconnect now, better safe than sorry.

[nancy1969]

I have additional question, do you have to use the "Safely remove hardware" when powering down a computer? I leave mine on 24/7 when home but during the week power it up whenI get home and down when I go to work. How do I power down the usb drive when shutting down?

[andy_the_actuary]

A peripheral reason to disconnect your disk altogeter is to avoid frying if your electrical system is struck by lightening. Do not depend upon your CPS or surge protector to safeguard your backup disk.