The un-format thread made me think of this one. How many times can you format or write/overwrite a hard drive before it starts to go bad, or is there such a thing?
How long is a piece of string?
Assuming no manufacturing defects and it lasts the first few months then you will have about a 3% chance it will go wrong in year 1 and about 15% chance that it will have had some sort of failure requiring replacement by the end of year 2. We have quite a few drives still going strong after 6 years. This is based actual records from where I work.
Typical harddrive MTBF ratings run between 300 and 500 thousand hours.
Chillihead:
Wow. Last time I saw statistics, the odds were 3% over 2 years for HDDs.
Out of curiousity, chilihead, are these PCs in a manufacturing plant, or an office, or certain other harsh settings?
the PCs are in a university. However I forgot that those figures included the Fujitsu MPG series of drives which had an alarming failure rate of about 30-40% within 2 years.
oops!
So, I’m guessing that they can be written/overwritten a good number of times before they wear through, so to speak? Are they like, say, magnetic tape in this sense?
Joe: They’re better than tapes. Hard drive platters are hard, made out of metal coated with a special magnetic layer to hold the charge. (Each metal disk is known as a platter, and there are multple platters to a drive.) The head doesn’t touch the platter itself (unless you experience the dramatic lossage known as a head crash) but rather reads and writes the charges from a distance of a few millimeters. There is much less wear and tear on a hard disk than a tape, given the same amount of data access.
(Tapes being plastic film permeated with a ferric (made of iron) substance that flakes off as the read-write head rubs against the tape in the process of reading and altering its state.)
I keep getting hung up on that “mean time between failures” over 100,000 hours. I mean, that’s about 11 years … what does that number mean anyway if it’s not that a drive will go for an average of 11 years before the first “non-recoverable error” (another term that they use to describe a failure)?
>> The head doesn’t touch the platter itself (unless you experience the dramatic lossage known as a head crash) but rather reads and writes the charges from a distance of a few millimeters.
a few millimeters?? I don’t think so.
I’m assuming he meant micrometers. We’re talking microscopic dimensions here, folks, and typically you’ll experience bearing or head failure; the media doesn’t wear out from being magnetized/demagnetized. Some HD platters are (or were-I believe IBM was the primary manufacturer doing this) made of glass rather than aluminum.
A good explanation of HD MTBF is here.
Sorry, I should have said that the medium doesn’t usually wear out. However, if it does, it would most likely be due to a defective magnetic coating rather than actual wear and tear, since, as noted before, no actual physical contact occurs between the heads and the disks.
Ah, that for the great information, everyone. previously, I thought that they were akin to, say, a record player… 
I shall use it to my heart’s content then.
Every now and then, particularly when there is a lot of continuous read/write activity, my hard drive (about 2 years old) will pause for a half second, make a clicking sound and then resume activity. So far it’s never been a problem except for when I am capturing video (several dropped frames will occur). Is this a sign that something may go bad on me, or is this normal activity? I’m hoping it’s just something like the drive switchig platters.
Clicking sounds are not normal, and are usually a sign if failure. The clicking will probably become more frequent and disk access become slower until it becomes unusable.
A normal reason for clicking is thermal recalibration. Check the specs of your drive on the manuf.'s web site.
Hard drive platters are usually Ni-Phos (amorphous) coated aluminum discs for fixed drives. Laptop drives are ceramic-based to withstand impacts.
The read-write head is mounted on an arm called a slider. The spacings between the heads and the discs are not in mm, not in microns, but nanometers. When the disc is to speed, the slider planes across the surface. The slider is designed so that bernouill effect lifts it from the surface. The surface? Between the magnetic layer and the heads, there are lubricants and tribological coatings (diamond-like carbon). Research is on-going to get rid of the these coatings, so that the recording will be contact.
The heads contact the surface of the disc rather frequently. It generally causes an asperity (thermal transient) in the head. These are worse for the head than the disc.
When do they die? In my experience, right after the 3 year warranty ends. The bad players in my limited experience have been western digital drives.