没有人愿意认为硬盘会坏，更不用说遇到问题了，但硬盘诊断工具如何真正知道扇区是否坏呢？今天的超级用户问答帖子回答了一位好奇的读者的问题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

图片由Matthew（Flickr）提供。

问题

超级用户读者David想知道硬盘诊断工具是如何判断扇区是否坏的：

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?

硬盘诊断工具如何知道扇区是否损坏？

答案

超级用户贡献者Stavr00和oletange为我们提供了答案。首先，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.

接着是Ole Tange的回答：

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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