Helping people with computers... one answer at a time.

External hard drives are convenient for many reasons. But should they be left on all the time? The answer's never as simple as you think.

I'm just curious if an external hard drive is less likely to die if you don't always keep it on and only turn it on for short periods of time a day? Because I have 3 external drives and I only turn them on when I need to use them instead of keeping them always on.

Short answer: no.

However, as is so often the case, the answer is never really that simple. It really depends on a bunch of other factors as well.

As it turns out, leaving a hard drive running isn't particularly harmful. It may be wasteful, but I'll talk about that below. Many computers have their hard drives running 24 hours a day seven days a week for years. A study by Google a while back concluded, among other things, that if the drive doesn't fail within the first year (so called "infant mortality") it's actually likely to have a relatively long and healthy life.

The "problem" with the Google study was that the drives were left on 24 hours a day, which doesn't reflect common consumer usage.

And here's where things get sticky: it's known that heating and cooling electronics like disk drives repeatedly does cause wear and tear. Exactly the kind of heating and cooling that a drive might experience when you turn it on only when needed. It heats up, you use it, you turn it off it cools down. Over and over again.

So that might make for an argument for leaving it on all the time, right?

Not quite. External hard drives in particular typically "spin down" or turn off after a period of inactivity whether you want them to or not. The next time you access the hard drive it spins up - the cause of the delay you sometimes experience after you haven't used the drive in a while - and then stays running until some time after you stop using it.

"Just how often are you using that drive, anyway?"

In other words, no matter what you choose to do with the external drives, they may already be doing something else.

And of course we need to factor in energy consumption to confuse things even more.

One of the big reasons that drives do spin down when they're not being used is not related to the drives at all, but rather the power that they use. It takes more electricity to keep the drive spinning that it does to just keep the drive electronics ready to go. So by stopping the physical drive you end up using less power. In fact this is often an explicit option in the power settings for laptops, though I know of no way to control it directly in most external drives.

And to be honest, keeping a drive running 24 hours a day if you only use it once a month is wasteful. Which introduces the final complication:

Just how often are you using that drive, anyway?

As you can see there's really no simple answer.

So I'll give you a rule of thumb: for most usage you're probably fine to treat your external hard drive as an integral part of your computer. By that I mean turn it on when you turn your computer on, and turn it off when you turn your computer off.

And because the drives are probably already spinning down on their own, whatever you choose isn't likely to make a huge difference.

As for me, well, I'm an edge case to be sure, but here's what I do: all my computers are on 24 hours a day. I have four external drives that I also leave on all the time. They're all used every night as part of my backup strategy and of course they automatically spin down during the day unless I happen to use them for something else. If they were used less frequently (say once a week) I'd be tempted to turn them off when not in use.

Article C3249 - December 27, 2007 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

December 28, 2007 6:51 PM

I've pondered this on end. Having worked for 25 years servicing disc drives (along with other equipment) I did observe that most failures in 'electronics' seem to occur on power down/up sequences. However 'mechanical failures' occurred more randomly.
Read/write heads actually float on a cushion of air created by the spinning of the disc. Older designs "loaded" the heads against the surfaces after the drive is spinning. Newer designs "park" the heads in a null spot until the drive starts up, but are always 'loaded'.
Ergo, starting and stopping the drive allows the head to land on the surface (wear on head) and exposes you to electronic failures due to power spikes.
BUT, constant spinning wears the spindle bearing assembly, and you can sometimes see (hear) this on older drives as they become noisier. The one advantage this choice offers is the likely-hood you will hear the increased noise and back up your drive before failure.
The greater concern in my mind, than either of these scenarios, is the constant scans performed by security programs which are 'pounding' drives relentlessly, day after day. The R/W heads are linked by tiny wires or film strips to circuits on the base. These electrical connections 'flex' with every repositioning. If you bend a conductor enough times---.
Not to be 'un-green', The power consumption issue would be offset by skipping one trip downtown a year. Probably for your whole PC if you live in a metropolitan area and wait in traffic! Roger

Carl R. Goodwin
December 28, 2007 7:49 PM

My "old" Maxtor drive, which was not even a year old, failed BECAUSE I turned it on and off every time the computer was shut down. The on/off switch failed, and I had to jiggle it to get it to run. My new drive, a W/D turns itself on and off with the computer, so there is at least no mechanical failure possible like there was with the Maxtor.

Domenic Cocozza
December 29, 2007 1:32 AM

If you dont have a fast connection USB it will take ages to 'Boot Up' when you switch on if your xternal hard drive is in the on'' mode: correct?

Eli Coten
December 29, 2007 10:20 AM

I have a Maxtor External hard drive and I've never seen it power-down. and I have left it turned on & unused for a long period of time. It also doesn't have an on/off switch for some reason.

Adrian Barrett
December 31, 2007 5:14 AM

I have three external drives, only the oldest a Freecom 120GB model has no switch and turns itself on and off with the computer. It was the first external drive I bought and contains DV video files I edit on Premiere so it is used either intensively, or not at all so the answer is to unplug the USB cable unless I specifically need it. Both the other drives have power switches.

In an ideal world with a multi-external drive setup we would be organised to have one set ot type of files on one drive (i.e. photos), another with a different type (office work, etc), and one for backups but the reality it it doesn't work that way as developing another arrow to my PC bow means I have hundreds of different filetypes.

Also, those handy personal external drives that work off USB power and now reach 160GB or more capacity will ALWAYS switch on and off with the PC/Laptop, so as these are more expensive in the first place are they economically viable with all that wear and tear bearing inmind the travelling wear and tear in a bag?

Keep up the good work, great site and newsletter!

Leo A. Notenboom
December 31, 2007 10:42 AM

Hash: SHA1

Domenic: not correct. The speed of your USB should only
affect your data transfer rate. The connection isn't used
that heavily when booting (if at all) - unless of course
you're booting *from* the USB device, in which case yes,
it'll be slower.


Version: GnuPG v1.4.7 (MingW32)


Leo A. Notenboom
December 31, 2007 3:10 PM

Hash: SHA1

My Maxtors (I have two) do not *power* down, but they do
*spin* down. Meaning that the lights stay on, but the drive
stops rotating. Biggest clue is that as soon as you browse
the drive beyond the root or current folder there's a 10-15
second delay as the drive spins up.


Version: GnuPG v1.4.7 (MingW32)


Bill Leeper
January 1, 2008 10:41 AM

I have a Maxtor external drive attached to my Mac and it doesn't seem to spin down. There is no delay when I browse three or four folders deep after it has been setting there for some time. The vibration level also seems to remain constant at all times. It should feel a bit different if there were just a fan running and not the drive.

James Fox
January 1, 2008 3:04 PM

One additional factor not mentioned was the role of power supply stability. Power surges from the AC line do not help, and brief interruptions (often due to lightning or bad weather) do not help the longevity of hard drives either. I use a ZeroSurge series filter plugged into the AC outlet to protect against surges, and a APC un-interruptible power supply plugged into the Zero Surge to protect against interruptions, with the PC of course being plugged into the APC.

January 1, 2008 3:53 PM

To Roger: Not all drives use the CSS (contact start/stop) mechanism you described. All Hitachi hard drives use a load/unload ramp, which causes no friction wear to the head. (Ramps can have other issues, however.) Seagate's 3.5" drives still use CSS, last I heard, so people who use that vendor may wish to avoid excessive power cycling.

Also, most spindle bearings are FDB (fluid dynamic bearings) so bearing wear isn't nearly as much of an issue as it used to be. Modern flex tapes generally don't have fatigue issues, either, at least from what I hear being in development. (I work in the industry.)

Other remarks: What does concern me is electronics wear with power cycling, since electromigration effects are greater as transistor size shrinks (current generation SOCs are 90nm). However, risk of head-disk interaction as a result of internal contamination, application of external force, or other issues (firmware problems, failure to park on an emergency power-off, etc.) counterbalances the argument to leaving a drive on all the time, since usage of the drive raises risk of HDI. Excessive heat due to the drive running can exacerbate thermal decay of written data, as well.

All drives will experience degradation of the magnetics because of superparamagnetism, whether they are on or off. This is a practical limit on the lifespan of a drive due to degradation of the once-written servo pattern. Copying data to an HDD and leaving it in the closet for 5 years is NOT safe -- I'd prefer optical media. (Just make sure to use a high-quality brand like Taiyo Yuden, not the cheap stuff, which can delaminate.)

In the end, because of the complexity of HDDs, the differences in models, and the difficulty of extracting probabilities of failure, whether to power down or not is still a matter of preference. I shut off most all of my HDDs when not in use, since I view the mechanical and magnetic risks to be greater than the electronics ones. Thus far, I've had good luck. If one chooses to leave a drive on all the time, definitely make sure it's well cooled. Multiple backups over multiple drives is the safe thing to do. Also, don't trust what the manufacturer says about drive life -- the one oddball failure on the Weibull projection could be the one with your data on it.

Thor Johnson
January 2, 2008 7:27 AM

A note on spin downs: Beware that Desktop HD's are rated notoriously low on spinup/down cycles (~3000 for a select few), so constantly spinning them up/down will kill them in short order.


Laptop drives, OTOH are supposed to have much better spinup/down specs...

George Arauz
January 6, 2008 4:36 AM

I own a Mac and with my external drive not having an on/off switch it doesnt really matter. My external is mostly for music and etc for my ipod but i dont see why turning it off would be essential anyway.

January 14, 2008 11:19 AM

Thanks for the information. I just bought an external IDE hard disk USB enclosure and installed an extra hard disk I had laying around in it. Te enclosure has an on/off switch, so I am contemplating if I should turn it off after I have powered down my computer or not. I am tempted to turn it off since my other hard disks are being cycled like this and they have had good life spans.

March 14, 2008 1:13 AM

** I am using an iMac
My external hard drive has been partitioned into 3 sections.

BEFORE I TURN OFF MY EXTERNAL HARD DRIVE - do I need to 'eject'each disk partition on the external hard drive - before I turn off my iMac ?

- Is it similar to 'ejecting' a USB storage device, before removing it, so as to avoid the LOSS OF INFORMATION, that can occur if you do not use this sequence before removing the device.

This information is not to be found in the user manual, and I get a little pissed off with these manufacturers in that they can be quite scant in the info they provide. Especially considering the consequences !!!

I would be truly grateful for a reply.


April 16, 2008 12:31 PM

Do hard drives shut down when my system goes into stand-by or hibernation? The Power Options on my laptop allow stand-by, hibernation and shutting down the hard drives after various lengths of time. If I have it going into stand by or hibernation after let's say 20 minuted idle, is there any reason to tell it to shut down the hard drives? Also, I have my laptop set to go into hibernation when I close the lid. I do this sometimes overnight and sometimes I do this for days at a time. Is this wise?

Leo A. Notenboom
April 19, 2008 10:46 AM

Hash: SHA1

Yes - disks powerdown durign standby, hibernation and of
couse, power off.


Version: GnuPG v1.4.7 (MingW32)


June 18, 2008 5:53 AM

Hi, I have a Seagate 300G external hard rive which works perfectly except:

1. When you turn it on it is fine.
2. When you turn it off and then turn on again (after any period of time), it doesn't turn on.
3. To turn it back on again, I take the power cable out and then put it back in again and it works fine.

This needs to be repeated every time I switch it off and on again without taking out the power cable.

The drive is about 8 months old and I have been having this problem for few months now.

Any ideas, why it is behaving like this?


January 1, 2009 9:41 PM

I have a 1TB Western Digital MyBook Studio Edition. Should I keep that on? I use it sometimes. It is mostly for storage....

Is it better to turn it off using the safely remove hardware or just hitting the power button on the drive?

Also, is there any part in the bios that allows Firewire on like USB Legacy support? Because I'm having problems when starting the computer, if the drive is on - it'll freeze and the Windows XP loading screen and just sit there for hours and never load... but when it is off it'll go through that fine.... I called WD but they weren't much help...


January 6, 2009 6:22 AM

This article is misleading and incorrect for many users.

Many of the most inexpensive external drives. Which likly make up the majority of external drives sold have NO power management system and will overheat and crash if use all the time. They run at full spin all the time.

non-savy user who just buy the cheapest external they can and don't do anything to keep it from overheating.will usally find that in will crash within 3-4 months.

Check the manual of your external drive. it will tell you what is your best corse of action.

August 18, 2009 11:31 AM

I have a WD 2.0 ext dr. It must be a very early model as it's not shown pon the WD product pages, it's several years old.
It doesn't shot down with the XP PC, the green light stays on. I put an ext on/off switch to the WD power supply. Don't like using this because the drive shuts down really hard.
Not sure it needs to be shut of at the power supply.
When it sits for some period of time and I fire up the beast some kind of bar red runs across the moniter. I now asssume the drive shaft has disconnected and is now reconnecting. After the red bar goes away the WD works.
Have had this unit for several years and it has always run when asked to.

October 6, 2009 4:08 AM

Hehe thats like saying should i leave my lights on when im a sleep it shouldnt matter but yes it all depends on what type of external you have if it has a fan it should do better than most if its a known brand even better but nothing lasts forever

December 1, 2009 6:16 PM

More a like a question ! my set up is hp 3.2 GHRTZ dual core WITH 2 HDD internal 250gig set up in raid 0 PREVIOUSLY it was 3 250gig UNTIL i got feed up of replacing them ( twice in 3-4 month ) AND I STILL KEEP 2 x 250GB . but added a 500gig NON raid internal.

fortunately I also have a HP personal media drive of 500 GIG, and also an hp media smarth server of 3 x 1TB ( tera )and one wd 250 as the software drive on my server.

NOW, aftr addind the 500 GB internal drive (non raid ), I HEAR A LOT of POWER UP and down ( is it because of vista power scheem ???? ) OR because I do not use all that space all at once ??? drive d internal is merely a bck up of more of important files on my 3.5 TB server )

BECAUSE I,m sure the server after some time will lose a drive... ( murphy-s law ) and bt the way I still have a internal sata port IN my CPu... wich i plan to buy a 2 TB internl ( in case of my server going down )

QUESTION ? why this non raid new drive keeps CLICKING on and off ???

Richard Fontaine
December 27, 2009 12:09 PM

My LaCie USB external HDD used to spin down after a period of inactivity. It doesn't do it anymore, spinning all the time. What changed ? There is no software other than a backup program for the HDD.

Ray Richardson
January 26, 2010 5:18 PM

I'm a subscriber to your newsletter. I've just purchased a 500 GB External Hard Drive.Now I know nothing about setting up and using them, so could you direct me to a source where I can learn from A to Z ? I'll be using it mostly for back up but also to store photos and music. Would you please help me get started? Thank You and My best to you, Ray

February 4, 2010 7:20 PM

my 500gb Western Digital MyBook is not reading the data correctly. I can see all of my folder with their titles, but when I click on them there is nothing in the folder. Is there some kind of tool or utility that will fix this? BTW, once upon startup, checkdisk started checking the hard drive and said there were errors. before I could stop the process it continued and then said it deleted some files that were incorrectly indexed. would this be the cause of my problem, and if so, what do I do now? I'm getting pretty frustrated with external hard drives. (I have had two others that have failed, but need extra disc space. what should I do?) Thanks for your answer.

March 26, 2010 1:36 PM

Turning external Hardrive on or off (While Computer is already running) occasionally causes computer to crash. have used external hardrives in this way for years without such a problem.

ONly 2 reasons I can think of:
1. Noticed the LED light on the external hardrive no longer is lit. Ive only noticed this around the time that this problem started. Perhaps a short in the light wiring?

2. A recent BIOS update and Windows repair install. The repair neccessary due to computer freezing, and has since ceased. (I believe the problem may have been due to a faulty RAM stick which has been removed).

Perhaps a change BIOS settings may be the cause of the crashing with the Ext Hard drive, (Unplug n play settings?)

XP Home
2G RAM 800 Mhz
INtel Q8200 1333FSB

April 4, 2010 7:30 AM

hi i have a amd 5700x2 vista ,i put a 120gig external drive on it for music ,i stream when playn songs i get a popup of the ext drive asking me where i want to play songs from realplayer ,windows media player etc ,but it popsup and stops the song being played ,how can i stop this from happening ,i tried to save music to realplayer but it keeps wanting me to play in windows media player ,i tried unplugging it to see if my songs are saved to my internal drive ,but then it gets red circleswith a bar on my songs and they wont play ,can you tell me how i can play without the external popping up and stopping the songs

April 23, 2010 11:44 AM


What I'm saying is that in the long run it probably doesn't matter either way. Do what you feel comfortable doing.

Just Me
April 27, 2010 2:08 PM

depends on the enclosure and what drive is installed in it, and how you use your system
I don't use my systems every day so I turn everything off at the end of the day

I've found that all of my external Hitachi disks go nuts and start making weird noises if they aren't powered off when the system is powered off

I forgot one day to power down 2 external disks (Hitachi) and woke up to what sounded like 2 jack hammers as the heads were being run back and forth over the platters for who knows what reason
and when I powered up the PC the noise quit but it starts up again if I don't shut them off when powering down the system

a good rule is: if you need it today, it's on for the day until the end of the day shut down,
don't just start it up for 5 minutes etc. to transfer files and then turn it off again, that will burn out the drives faster than leaving them on until they die

running the disk for only a few minutes at a time
is about the same as while driving a car, putting it in neutral and shutting it off for every hill you go down, you'll eventually burn out the starter etc.

you need to disable Autoplay & Autorun
your shortcuts / playlist etc. will start playing the file before the autoplay & autorun file sniffer finds all the files but as soon as it finds them after snooping the drive it interrupts the current file being played while it waits for you to decide what you already decided

September 8, 2010 4:46 AM

I'm bought a new external hard drive a week ago. It is 1TB. I have never used an external hard drive for anything before. I have always burnt things to disks, and only bought a hard drive because my DVDs were corrupting.

If I turn off the power with the external hard drive, does that mean that all the data on it will be erased? Or can I carry it around and use it, only plugging it in to read the files?

It's a hard drive, which means what's written to it will remain even when powered down. You can take it from computer to computer, just remember to use "Safely Remove hardware" if the computer is running to safely remove it.

September 10, 2010 5:37 AM

Hey, thanks a lot for writing this!

I would ALWAYS turn off my external hard drives immediately after I copied something to it. I've had 3 of the fail within a year.

I don't know if that's what caused them to fail but now I can eliminated it as a potential cause.

jerry randall
January 16, 2011 8:30 PM

great site leo!! i too am an edge case. i have 7 external hard drives spread over a 3 computer set up and a few things have come to mind. one: some of my drives don't have an on off button, so they just start up when i used to turn on my outlet strip....the others i had to reach under and turn back on... minor inconvenience. i have had drives burn out by the constant daily on-off thing. so 2 years ago, i decided to leave them on... remembering years of electronic retail where televisions and other display items were on 24/7 for 5 to 6 years and never burn out. So, because i do music production and i'm always back and forth from home computer to laptop( both for music) and sometimes on and off 2 or 3 times a day i just decided to leave them on. and so the only worry is will they just crash i'm always backing up to the newer ones...and buying newer ones as i go.

Scott from Boston
March 10, 2011 5:05 PM

I'm looking to buy an external hard drive. I take a lot of family photos, (about 12,000 per year) and don't want to lose any. My biggest fear is that I'll load all of my pictures onto the drive and then it will fail and I'll lose all of the pictures. What are your suggestions?

Do what I did - get TWO drives and then regularly make sure that they both work and contain the same things. ANYTHING that you have stored in only one place is at risk.

Larry Lester
March 14, 2011 4:53 PM

If I use "Safely remove hardware" as you mentioned above to temporarily remove my external drive, at a later date do I have to reinstall software if I want to reinstall the drive or can I just "Add hardware" with all software hopefully still in place?.

Safely remove doesn't uninstall software. Next time you plug your device in it should just work.

steve siegel
March 19, 2011 5:16 PM

I like to turn off my external hard drive when not in use, but want to do it safely. When try, using the "safely remove external device" icon (Win 7), I always get the message that the drive is in use, and cannot be removed. I assiduously have turned everything off first on this data-only storage drive, but must be missing something. Is there any way to look at what is actually running on a drive?

Bobby King
April 2, 2011 12:10 AM

Hey I would like to interject something here --and that is the words "load-cycle-count". If you know what that means than you would probably want to turn your units off when not in use. Many of the WD external units are set around 300,000 which in my world would only last around 6 months of spinning up and down. So I just need to figure out what External drives have larger load count cycles and also try and find a more quality drive.

August 8, 2011 9:12 AM

I have an external hard drive that i use for movies. When I was downloading some movies to the drive I unpluged it and try connecting it to my wd tv and it did not work. I later found out that the power cord had shorted. I constantly turn it off and on cuz I continue to put movies in it. I s there a better way?

November 3, 2011 12:47 PM

I have ONE external hard drive connected to a seperate power adapter-when i want to power off the PC-do i switch off the Mains Power Supply altogether or should i power off the External Hard disk FIRST before i Click the " Power Off Computer " then Power Off Mains Supply ?

I'd shut down the computer first, then the external drive, just ot make sure that the computer had finished doing whatever it needed to to the external drive.

February 6, 2012 2:56 PM

Hi Leo, Does the spin down cause an increment of the S.M.A.R.T variable PowerOnCount? Or is it only when you actually turn the drive off and stop power going to the drive-tronics?

Dijait Evans
February 19, 2012 5:42 AM

Ok, it's interesting that this article was posted in 2007 and you're still getting questions on the subject. I have an older iOmega external HDD. I've had it for at least since 2007 and I've never done anything to turn it off. It is USB but has its own power supply. So does it spin down by itself or not. There are times I can hear it doing something. If I touch I, I can feel it. I guess I'm thinking, that after reading these articles, if it stays on it should have burnt out by now. but it works fine. Please explain, because I'm now starting to worry about it too much.

Some do spin down, some do not. If after not using it for a while it takes a few seconds for the next access to work, it might have spun down. Even if running continually for 5 years I wouldn't worry excessively. (If drives survive the first year they can last a long time, statistically.) Any drive can fail. Backup your data and sleep soundly.

March 24, 2012 12:01 AM


I got a question? I have 2 2tb hdd's and one i have had for at least 2 years and runs fine and it is filled up(about 450gb's left) and my other i just bought about 4 months ago but i just am now starting to use it but i did a stress test and everything when i first got it and it did fine also ,but for some reason when i start watching the movies i have on it or when the computer goes to sleep and it turns back on the drive messes up. When the computer wakes back up the hard drive freezes and the accesses lite just stays on and when im watching a video the hard drive like stops work all together(it doesn't freeze its like it shut its self off) the disks stop spining and everything and the only way to get it working again is to unplug the power to it and power it back on. I notice that is the only time it happens but if im transferring files it never happens.

could this be a hd problem or windows messing with me?


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