Talk:Bad sector

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I hereby release the second paragraph of this article to the public domain under whatever license wikipedia desires. (metiscus@gmail.com)

Not accurate

"A bad sector is a sector on a computer's disk drive or flash memory that cannot be used due to permanent damage" this is not accurate as for example Windows can in accurately deem a sector a "Bad Sector" and relocate it when this is not always the case when a thorough tool such as Spinrite is used to thoroughly test, "bad sectors" that were incorrectly detected (by Windows for example) can be brought back into service if they should not have been marked bad in the first place. (See GRC.com for further information). I added a hastly worded addition after that but not intende for it to remain... just that the statement is not correct without a qualifier. —Preceding unsigned comment added by 68.115.74.106 (talk) 06:46, 6 May 2010 (UTC)

Spare sectors

"When the operating system begins to detect bad sectors, in most cases, it means that the surface of the hard disk is failing and the drive has run out of spare sectors with which to remap the failed sector."

This may be true for write-mostly workloads, but on a typical desktop computer bad blocks are detected by the OS very quickly, long before the drive runs out of spare sectors. The drive may run out of spare sectors without the user noticing if it works in a replicated configuration, and there are other good replicas of the unreadable sectors, and the OS or RAID controller detects it, and remaps it by rewriting unreadable sectors with good data. I don't know which RAID solutions do it. All RAID systems I've seen just kick the disk out of the array as soon as any read error is detected, which usually means the disk gets replaced long before running out of spare sectors. 62.121.97.188 (talk) 22:16, 13 August 2009 (UTC)

How many spare sectors does a disk generally have? I figure it probably depends on the size of the disk, but what's typical for let's say a 100 GB HD? Frederik Holden 16:44, 30 October 2007 (UTC)

Around few thousands of 4kB sectors, according to SMART. Google "reallocated_sector_ct FAILING_NOW" for some SMART reports. 62.121.97.188 (talk) 22:16, 13 August 2009 (UTC)

Hard disk sectors are 512 bytes generally (but it may be 256,1024 or more). So for a 100 GB hard disk (which is 107374182400 or 1024^3*100 bytes) you would have 209715200 sectors (107374182400 divided by 512). —Preceding unsigned comment added by 64.81.166.246 (talk) 21:40, 14 March 2008 (UTC)

Oops - I didn't read your question very carefully. How many SPARE sectors does a drive have. I could not quickly find amy information on this. I'd bet it's a risk vs. reward system with the HD manufacturers. They'd want the most storage for the least amount of sacrifice of physical drive space to be able to offer the most competitive price. Perhaps higher-end (server) drives have larger spare sector areas. Nothing to substantiate any of that, however. —Preceding unsigned comment added by 64.81.166.246 (talk) 21:47, 14 March 2008 (UTC)

The Amount of spare sectors depends on the drive size a 500 gb hard drive you only get 465gb the rest is spare sectors.Shipmaster117 (talk) 10:04, 14 January 2009 (UTC)

not really, that difference is because of the 1000 vs. 1024 counting of the hdd manufacturers vs. operating system. —Preceding unsigned comment added by 92.226.192.102 (talk) 15:44, 26 March 2009 (UTC)

Good question, Frederik Holden.

There's a vague statement of a "spare sector pool ... of thousands of reserve sectors" at hard disk drive#Error rates and handling. I've heard similar statements at various times in various places -- anyone have a reliable source for the size of the spare sector pool?

I'm not even sure a "spare sector pool" is the best way to describe what modern hard drives actually do. I've heard some people say that they've heard a friend of a friend say that the hard drive manufacturers don't bother with individual spare sectors anymore; recently (?) they fail and remap entire tracks to a reserve pool of spare tracks. What's really going on inside there? --DavidCary (talk) 20:59, 20 January 2014 (UTC)

I don't think they remap an entire track at a time; rather, they set aside an entire track for remapping. I think somewhere in the SCSI-related manual pages I read that the "spare pool" may be split by the vendor so that only nearby spares can be used for remapping, but I am struggling to find it. Artoria2e5 🌉 17:15, 27 May 2023 (UTC)

Intentional bad sectors

The "intentional bad sector" method of copy protection dates back to the days of floppy disks on Apple ][s, TRS-80s, etc., and possibly further. Not sure if it's worth a mention in the article though, since CDs and DVDs are now by far the most common methods of non-network distribution. Nibios (talk) 19:42, 21 May 2011 (UTC)

There is lots of missing info about intentional bad sectors, as well as wrong info. The technique of storing two sectors with the same number on the same track (twin sectors) is not a bad sector technique at all, as both sectors are valid. One technique for checking them was to seek a specific sector before checking the protection, then seeking a different sector before reading the protection sector a second time. both reads of the protection sector are then used unchecked as decryption keys. Furthermore, the lengths of the sync on that track were adjusted to non standard lengths. Since even a nibbled copy containing both copies of the sector on the usual unmodified disk drive will have different sync lengths, the wrong copy of the twin sector will read one time or the other, and the loader will fail to decrypt and crash. Some tolerance was allowed for variation in drive speed. relocating the second copy of the sector to a different track and patching the loader to look at the second track for the second check defeats the protection. I've personally did this for a c64 game that used this scheme. 74.211.60.182 (talk) —Preceding undated comment added 08:38, 28 November 2016 (UTC)

Could someone please add this information to the article?

HDD Regenerator from http://dposoft.net/#b_hddhid is "sort of" the only such software out there that really regenerates bad sectors and renders them usable afterwards, EVEN THOUGH they might be phyisical bad sectors.

I learned from friends that there are two kinds of bad sectors, logical and physical ones, and that only the logical ones could be repaired as they are digital while the physical ones could not be repaired by software as they were physical.

I have now come to understand that what I have been told by friends is wrong...

Thanks! — Preceding unsigned comment added by 86.125.191.144 (talk) 11:05, 19 December 2011 (UTC)

Well uh, back in China we use DiskGenius for the same thing. Same kind of stuff: big-block read to find rough failure locations, detailed read to minimize the range, and write. Artoria2e5 🌉 17:16, 27 May 2023 (UTC)

Eventually

The bad sectors are not recoverable unless I replace the storage device. They are only marked as bad and thus skipped. Right? But the soft bad sectors seems to be easily recovered because it is just something like wrong mark. --Euna8815 (talk) 03:20, 14 December 2013 (UTC)

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