Defective blocks or sectors

In general, a user changes his hard drive every 5 years, unfortunately it arrives sometimes that the hard drive which contains our invaluable (or not) given ends up weakening before this period. Most of the time, of the “extreme conditions” of use (too high temperature, too important activity, no maintenance carried out) are quoted like primary reason of failure.

The study undertaken by Google gives us more details on this subject. Presented at the time of a conference on “the files and technologies of storage”, the report/ratio of the firm with great G concludes that an hard drive can return the heart for reasons as various as varied.
At present, Google would count more than 450.000 waiters, the majority would use hard drives “general public” with capacities going from 80 to 400 Go. The study of Google would have related to more than 100.000 discs which entered under operation during or little time after 2001. These discs 5400 or 7200 turns/minute would come “from various large manufacturers of discs and would gather new principal models”.

To make a its study, Google would have consulted the whole of “vital” information which it would obtain from its waiters. Frequently updated information, at a few minutes of interval. In this field, one can in particular quote: temperatures, levels of activities or parameters SMART (Coil-Monitoring Analysis and Technology Reporting), often used to detect/prevent problems to come on an hard drive.
Google noticed, without surprise, that the rate of hard drive weakening with tendency to increase as the disc ages. During the first year of their actuation, 1.7% of the 100.000 hard drives used by Google would have being thus replaced. This percentage would have passed to 8% during the second year and 8,6% during the third year. Once entered its fourth year of life, Google affirms that the remaining lifespan of the hard drive “is more influenced by the model/mark that by its age”.

The problem of error of “subjacent task” of closing is often related to the defective blocks or sectors.

From which do they come?
It is about a all the more frequent manufacturing defect as the capacity of the discs reaches phenomenal proportions today.
A partition of disc is a volume. This volume is made up itself of several circular plates themselves segmented in blocks which one calls the sectors.

How much blocks is there on an hard drive or a volume?
A current disc contains almost 2.000.000 of blocks by giga is almost 2.000.000.000 (two billion) of blocks for a disc of 1 terabyte.

Surfaces of storage in full evolution, 1998 and in the same volume, an hard drive of 500 Mo sheltered only one unhappy million blocks.

For that it is necessary to add the collapse of the costs: in 1998 a disc of 500 Mo cost in francs the equivalent of 280€, whereas one finds today and at all the discounters, of the discs of 1 To for 115€, which makes fall the price the gigabyte of 560€ to 0,12€; not badly in 10 years!
If we applaud the technical performance, reliability did not follow the same course alas…
With a dimension reduced in such proportions. The sectors weakened, and their number in permanent growth increases the risk to find the defective ones.

A bad block, it is what?
A defective block is a sector (512 bytes) on which magnetizing (the writing) is not done correctly, therefore on which the files can neither be written, nor read correctly.

Consequences of the bad blocks:
Apart from the risks of loss of data, more they are numerous and more the disc is delicate to repair, a disc which has some much is trailed literally, the more so as their site is important, if they is at the head of partition it is straightforwardly catastrophic, because one can have split a Bitmap volume of which part of the data was moved on the zone of reserve…

How to prevent this kind of incident:
The manufacturers of discs advise to leave permanently at least 10 to 15% of free.
Carry out a regular maintenance of your disc.
To make safeguards on an external disc, dvd, you can also create an image disc of your system which will enable you to find your configuration if you must change discs.

Setting does not keep for the treatment of your disc with Filevault and the blocks defective.
Filevault encrypte your account user in only one and single file.
If your encrypté account occupies only one and single block on several million blocks, your file-image will be incomplete, the encryptée image of your account will be irremediably damaged without any hope to even recover though it is, not the least file!

Conclusion
The defective blocks are a big problem. Admittedly the Apple system is able of in réallouer much, but if the number has suddenly become extensive, Mac is not able any more to manage them and the restarting is often not possible and the hard drive is changed.