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Summary: 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.
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. Related:
• Recent Comments
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. Posted by: Bill Leeper at January 1, 2008 10:41 AMOne 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. Posted by: James Fox at January 1, 2008 03:04 PMTo 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. 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. [https://bugs.launchpad.net/ubuntu/+source/acpi-support/+bug/59695] Laptop drives, OTOH are supposed to have much better spinup/down specs... 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. Posted by: George Arauz at January 6, 2008 04:36 AMThanks 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. Posted by: Bob at January 14, 2008 11:19 AM** I am using an iMac 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. John Posted by: John at March 14, 2008 01:13 AMDo 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? Posted by: Lois at April 16, 2008 12:31 PM-----BEGIN PGP SIGNED MESSAGE----- Yes - disks powerdown durign standby, hibernation and of Leo
iD8DBQFICjABCMEe9B/8oqERAt6rAJoD5HH9iN4b37kdHScXJsMVazPNWgCfXsPw Hi, I have a Seagate 300G external hard rive which works perfectly except: 1. When you turn it on it is 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? Thanks. Posted by: Mohammed at June 18, 2008 05:53 AMPost a comment on "Should I turn off my external hard drive when not in use?":
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