When using hard disks as inactive storage, what is best amount of disk activity?

Hard drives are a reasonably cheap way to store a lot of data, and have other advantages. I am considering using them as backup media for long-term storage. I've heard that if I disconnect a hard drive and leave it on a shelf somewhere, I can expect them to degrade to unusability over the course of years. And an actively used drive gives out in maybe 2-5 years. Can you suggest a strategy for prolonging the life of the drive as long as possible? Ideally, the drives provide a reliable "restore" for decades. Minimizing power consumption is also a goal.

To give a concrete idea, I am thinking something like: Put all the inactive drives in computer cases, and fire the systems up once a month (week? year?) to give the drives some "exercise" and run checks for corruption.

There's not a lot of definitive information about hard drive reliability. There's Google's study, but that concerns lifetime of drives in use.

In addition to media degradation, when you're talking about long-term storage, you need to worry about technological obsolescence. WORM media were supposed to last at least 50 years, but in order to read an old WORM disk now, you'd have a hard time finding a drive. Similarly if you have an old RLL drive, it might be fine, but you'll have trouble finding a controller to plug it into.

As voretaq said, "you can't win." I'd phrase it as "there's no current technology that will let you store data for a long time with no intervention." If you want to be sure your data is safe, you'd better keep multiple copies, preferably on multiple media, and you'll have to periodically move the data to newer media.

About the only short-term advice I can give is to buy the most reliable drives you can afford. I've had good results with HP's drives and with WD's RE drives, vs. having a lot of WD Caviar desktop drives fail over the years.

I haven't heard of this, which doesn't mean it isn't true, but is that from a reliable source? I have PCs that I didn't turn on for years, and they were fine when I did. Also, I have heard that about CDs as well, and have binders of old burned disks which are all fine (CDs are built to withstand some loss of data though).

If it just that some of the sectors might degrade, I would just use par to create some recovery information to be on the safe side. You could of course you a RAID mirror as well.

Re: Do inactive hard drives really degrade? I haven't heard it from anywhere official or particularly authoritative. The information I have is that the bearings in a drive can dry out if I leave the drive powered off for a long time. And then when the drive is turned back on, I guess the bearings would be frozen up and the drive is dead. I don't want to spread misinformation--I'm not sure if the above is the truth or not.

Enterprises go to great lengths to ensure that not only their tapes last for 10 years:

• the drives to read the tapes
• hardware with the correct attachments and interfaces
• drivers and software capable of both reading the tapes and interfacing with existing and future systems.

The failure rates of hard drives may be much higher than other components in a PC or server, however I suspect the combined failure rates of all the components may in fact be higher than that of hard drives.

I don't think there is a silver bullet for long term storage, in my mind a solution would have several layers of redundancy (RAID, Hot Spare and/or Spare Parts) and be upgraded throughout its life to ensure the accessibility of the data.

Re: prolonging disk life, here are two equally valid yet totally contradictory schools of thought:

• Do not power or spin the drive at all unless you are doing a restore
  This is based on the theory that most hard drive failures are mechanical in nature, and that by not running the drive you don't induce any wear on the mechanical components, so when you need to spin the drive up again in 10 years it's not all worn out.
• Keep the drives in an array, powered up and spinning 24x7x365
  This is based on the theory that most hard drives fail trying to spin up after a period of inactivity, so rather than allowing the drives to sit and potentially bind up you just keep them in constant motion.
  As a side-benefit modern drives will constantly be running their SMART tests and if you're monitoring that information you'll hopefully get advance warning of an impending failure.

What you mention above is a hybrid that I would consider to be the worst of both worlds: The drives are being spun up and run periodically (so they're getting mechanical wear), then being spun down and stored (giving them the opportunity to bind up and refuse to spin ever again). To add insult to potential injury I'm assuming the drives would need to be moved to and from storage (bumps shakes and jostles = more potential for failure).

In reality you can't win: Even traditional tape backups are subject to the tapes degrading with age, or the one and only drive that can read tape X finally dying. Best advice I can give is have more than one archive (preferably in different formats - e.g. HD & tapes or HD & DVDs), store them in good conditions, and hope for the best...