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I have 2 external drives which have some bad sectors, model Samsung G2 portable of 640 GB. Both are no longer under warranty as they are more than 3 years old. Naturally, I moved all my important data on another drives. But, since the number of bad sectors is (or, more exactly, was) not very high, several hundreds at most, I intended to keep using them (for "junk" data, which I would not care about if it is suddenly lost) until they would simply fall apart.

I had once a hard drive (internal) which showed bad sectors and I was able to use it intensively for more than 18 months after the first bad sectors appeared. But here is a little problem: I reformatted both drive in order to have the bad sectors marked as "bad" and re-allocated. But, while the bad sectors dissappeared after the reformat, the reformatting resulted in several sections of the drives (tipically of 5-10 GB in size) becoming extremely slow. One of the drives showed bad sectors almost 2 years ago. Reformatting removed them and no new ones appeared, but there are small parts of the drive where the writing speed slaws to a crawl (up to 1-2 MB/s). The reading speed is fine over the entire drives. The second drive (which went bad just a week ago) again had no bad sectors after reformat anymore and its health status is labeled as ok by HDTune Pro (the tool I use for drive diagnostic), but there is at least one part of the drive where the reading speed, this rime, becomes very slow. The part is at the position 48-54 GB on HDTune's drive map and the reading speed slows down there to 4-5 MB/s. The writing speed is fine over the entire drive.

Is there any way to fix this? Not to repair the damaged sector (that is pretty much impossible most of the time), but at least to mark the slower sections so that Windows won't try to write there. The drives are still usable; the first which went bad had been stable for more than a year with constant usage, but this speed problem can become irritating when you hit the faulty sections.

Any ideas?

PS: I have replacement drives and I intend to use the faulty drives for data I don't actually care about. Basically, I want to give them a go until they fail for good. Moreso, I am not certain that the drives were doomed, so to speak. One of them kept functioning for 2 years after it developed some bad sectors. By most accounts, this is very unlikely to happen in case of physical bad sectors. In addition, the bad sectors disappeared after being rewritten and physical bad sectors can't actually be mapped out by conventional diagnostic/repair utilities. If the bad sectors my drives developed were logical ones, then the drives are still very usable. They do continue to work, but they only have a problem with the speed (one drive with the writing speed, the other with the reading speed) over some small portions, which I can't figure why and it's a bit annoying.

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    Have you considered using fdisk which, I think, let you choose sectors to write for a partition, and exclude the bad ones ? I have no idea if it can work, but hey, who knows ? – MrVaykadji Jan 6 '14 at 22:18
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Likely you reformatted on MegaByte boundaries. Re-reformat on cylinder boundaries for better speed.

The cylinder is a physical stack of all the same-numbered sectors (slices) across all platters (visualize a stack of pies, all with the same sized slices,, all lined up).

A MegaByte (MB) boundary does not physically align with the slices, and although using MB boundaries on an SSD is OK, if slows things down on an HDD.

GParted makes setting this up easier and here is an illustration.

  • Another method would be to partition the drive so that the bad bits are in a separate partition. – Wilf Jan 6 '14 at 22:36
  • Guys, thanks for your answers, but could you please be a little bit more elaborate? I do not know what fdisk is, what's the difference between Megabyte Boundaries and Cylinder Boundaries or how to partition the drive so that the bad bits are in a separate partition. – Delpino Jan 6 '14 at 22:57
  • But Gparted does not do full formats though. So, even if I set it "aligned to cylinders", would that work since Gparted performs basically what is the equivalent of a quick format? – Delpino Jan 7 '14 at 15:22
  • When you use Gparted to align on cylinders, then reads and writes are faster. So, do the fdisk full format first to block out what is bad, and then cylinder-align with Gparted for max speed. – K7AAY Jan 7 '14 at 16:39
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    As I specified, I did a full format with the Windows utility in the disk management. That blocked out what was bad and now all the diagnostic utilities report the drive to be fine (HDTune Pro and Windows Chkdsk). There have been no further bad sectors on full scan. But this reformat left me with a small section where the read spead is bad. The speed is assymetrical (reads slow, writes fast). On an older drive, it was the opposite (some sections with slow writing, fast reading). I did realign on cylinders one of the drives, but it had no effect. Is fdisk a more efficient tool in this regard? – Delpino Jan 7 '14 at 16:55

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