Miscellaneous/hdd-lifetime

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 How long will my Bubba HDD last?

So, your bubba have been running for a couple of years, how long will it last? 

There is not easy answer to that question :(


There are alot of metrics around, MTBF, CDL, AFR


WD (Excito's main HDD vendor) used to quote 30,000 hours of MTBF. But all that really means is that if you had a large sample of drives, half of them would be broken after 3.4 years.


Another example, using Googles "real world" AFR data (link 2 below), the AFR for the different disk ages:

Google AFR numbers

Disk Age

(years)

AFR
1 1.7%
2 7.9%
3 8.6%
4 6.1%
5 7.0%


So if you have a server room with 1000 disk, you could expect 1.7% (or a total of 17) of them to be broken after year, a total of 96 after 2 years etc...

Conclusion

  • A HDD vendor can't guarantee how long a single using will last, it's all statistical data. This data is only really meaningfull if you have a big array of disks, and doesn't apply very well (with great level of certainty) to your single datapoint (your bubba).
  • Disk MTBF numbers significantly understate failure rates.
  • Consider replacing 3 year old disks, or at least get serious about back up.
  • SmartMonTools will alert you to some issues, but not most
  • High/low usage and ambient temperature doesn't have a massive impact on HDD life


  • Most importantly Remember to always backup data you care about (pictures, docs, hg repos etc).
    Rule of thumb I use is to have them on three places, and all of them can't be in the same geographical spot (not all in same closet in the same house!) :-)


Some links

  1. WC Official Statement
  2. Google's Experiences of BIG disk arrays
  3. Why big MTBF numbers are pointless
  4. More on MTBF