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There has been a question about whether it improves your computer's performance - my question is based on the precept that magnetic audio and video tapes, for example, quickly show damage if data is over-written many times: a computer engineer I met introduced me to the idea that since a PC's hard drive is a form of magnetic data storage, it too will suffer from needless re-writing, especially when done routinely and therefore overwriting the same sections of the drive.

Defragmenting seemed more important with smaller HDD sizes, is it now a damaging practice we can do without?

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I strongly suspect your perception that magnetic tape wears out on reuse has to do with the fact that there is physical wear as the magnetic coating is dragged across the read/write heads. Hard drives, in contrast, do not involve physical contact between the heads and the magnetic coating. The heads float on a layer of air. –  MετάEd Nov 28 '11 at 23:28
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the drives do however contain mechanical components that eventually wear out. Think of the mechanisms to spin the platters and move the heads. Of course you'd need to test whether a constantly fragmented drive (which needs more moving to get to the read/write points) wears out faster than a regularly defragmented drive of the same type, and do that for a very large sample size. –  jwenting Nov 29 '11 at 6:52
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It is quite true that mechanical parts wear out, but not true that the magnetic substrate wears out as supposed by the OP. Under normal operating conditions the bearings will go long before you have any trouble with the heads or platters. –  MετάEd Nov 29 '11 at 7:32
    
I also heard it'll wear down your RAM –  ratchet freak Nov 29 '11 at 19:59
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closed as off-topic by Oddthinking Jul 18 '13 at 4:19

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2 Answers

Google published a paper on drive failure based on analysis of their use of over one hundred thousand drives.

Failure Trends in a Large Disk Drive Population, Eduardo Pinheiro, Wolf-Dietrich Weber, and Luiz André Barroso , Proceedings of the "5th USENIX Conference on File and Storage Technologies".

One aspect they looked at was whether disk utilization affected failure rate:

Overall, we expected to notice a very strong and consistent correlation between high utilization and higher failure rates. However our results appear to paint a more complex picture. First, only very young and very old age groups appear to show the expected behavior. After the first year, the AFR of high utilization drives is at most moderately higher than that of low utilization drives. The three-year group in fact appears to have the opposite of the expected behavior, with low utilization drives having slightly higher failure rates than high utilization ones.

One possible explanation for this behavior is the survival of the fittest theory. It is possible that the failure modes that are associated with higher utilization are more prominent early in the drive's lifetime. If that is the case, the drives that survive the infant mortality phase are the least susceptible to that failure mode, and result in a population that is more robust with respect to variations in utilization levels.

Another possible explanation is that previous observations of high correlation between utilization and failures has been based on extrapolations from manufacturers' accelerated life experiments. [...] Taken as a whole, our data indicate a much weaker correlation between utilization levels and failures than previous work has suggested.

So, if your fear is that the extra work being down to defrag is likely to kill your disk-drive earlier, it seems that it might cause a borderline drive to fail earlier. However, this isn't a strong effect.

Another effect might be observed: If a drive has a lot of read operations per defrag, then the time saved in seeking the right block will add up, and effectively reduce the overall utilization of the the system. If there is frequent defragging, but no other use, it will obviously increase the overall utilization.

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What has utilization to do with fragmentation and defragmentation? Since the paper is from a USENIX Conference and Google, I woulnd't even expect a filesystem which needs defragmentation is involved. –  user unknown Nov 30 '11 at 17:43
    
@userunknown: The OP is effectively speculating that defragmentation -> higher disk utilization -> worn out hard-drives. I use the Google paper to show that the latter link exists, but is weaker than expected. I also suggest the former link depends on how the drive is used. –  Oddthinking Nov 30 '11 at 23:29
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Maybe you remember the discussions about limited P/E-cycles for USB-flash-drives, which are limited to about 100 000 cycles, in contrast to normal hard drives, where you don't have to think about it.

Jonathan Thatcher, Fusion-io; Tom Coughlin, Coughlin Associates; Jim Handy, Objective-Analysis; Neal Ekker, Texas Memory Systems (April 2009) (pdf) http://www.snia.org/forums/sssi/knowledge/education/SSSI_NAND_Reliability_White_Paper.pdf

Another limitation is that flash memory has a finite number of program-erase cycles (typically written as P/E cycles). Most commercially available flash products are guaranteed to withstand around 100,000 P/E cycles, before the wear begins to deteriorate the integrity of the storage.[8] Micron Technology and Sun Microsystems announced an SLC NAND flash memory chip rated for 1,000,000 P/E cycles on December 17, 2008.

Even if you would defrag you flash drive on a daily basis, you could do it for about 30 years. Now consider that NAND-flash would allow it for 300 years, and this is worse than what you have to expect on regular hard drives.

If you write to a /tmp directory, or to a pagefile, you do so much, much, more often than once per day.

Conclusion: You don't have to think about it.

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