Днешната сесия за въпроси и отговори ни идва с любезното съдействие на SuperUser - подразделение на Stack Exchange - обединяване на уеб сайтове с въпроси и отговори.
Снимката е предоставена от Матю (Flickr).
Въпроса
Дисплеят на SuperUser Дейвид иска да разбере как диагностичните инструменти на твърдия диск знаят дали секторът е лош:
When I run across a hard-drive that may be failing, I scan it using ViVARD, which reliably lets me know if the hard-drive needs replacing or not. How do these sorts of tools work? How can they tell a bad sector from a good sector?
Как диагностичните инструменти за твърди дискове знаят дали секторът е лош или не?
Отговорът
Сътрудниците на SuperUser Stavr00 и Ole Tange имат отговор за нас. Първо, Stavr00:
Modern hard-drives implement a system in firmware called S.M.A.R.T. which collects statistics on the hard-drive’s performance and automatically avoids data loss by moving data away from bad sectors.
Diagnostic tools query the hard-drive’s S.M.A.R.T. software in order to build a health check report. Bad sectors are detected upon accessing the hard-drive, avoided, and necessary relocation is done by the S.M.A.R.T. system.
Последвано от отговора на Оле Танг:
I am not familiar with ViVARD, so this is a general answer.
S.M.A.R.T.
S.M.A.R.T. is a part of most modern hard-drives. It registers when the hard-drive sees a bad sector and when the ‘seek or spin up time’ is longer than normal. These are all indicators that a hard-drive is failing.
The way the hard-drive salvages a failing sector is due to error correcting codes (usually Reed-Solomon) that can perform a rescue if a few bits are wrong. If many bits are wrong, then the hard-drive tries salvaging by reading the sector over and over again. When it finally gets it right, it saves it to one of the spare sectors.
Reading Sectors
The hard-drive reallocates sectors with read errors to a set of spare sectors that are reserved for this. The operating system does not usually see this, but sees the whole hard-drive as having no errors. Only when there are no more sectors to reallocate to (or the sector cannot be salvaged) will the operating system see the broken sectors.
But it is possible to bypass error correction. I believe it is different for each model, but maybe ViVARD does it? This way you can read the actual data on the hard-drive. By reading this you will be able to see which sectors have errors, even if the operating system itself sees no errors.
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