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Archer's Guide to
Nine Lives to your Hard Disk

Release date: July 25, 2004

Lot of experts and not so experts say that once a bad sector has developed rush to back up your data and buy a new hard disk.

Not me, though. I have been using disks with bad sectors for years by using some tricks. Not that I cannot afford a new disk; I have too many, in fact. It has been a sort of a challenge to do such things and derive some satisfaction out of that

A colleague of mine always buys two of any gadget he fancies - one to use and one to break open and see how it is made. Well, some are like that.

Shall we begin?

A little of my pet theory first. I do not think that a sector suddenly loses its magnetic properties. In my opinion a bad sector normally results when there is a physical damage at that sector, may be due to a little grit that somehow escaped all precautions at manufacturing time and happened there. Once that sector is identified as bad, it is marked bad by the format program and no data is written to that sector afterwards. Ok, that is clear.

But each cylinder has numerous sectors and when the head tries to read any sector in the cylinder having that damaged sector, the head passes over that bad sector too but not reading it. The physical damage here may result in the gap between the platter and the head getting reduced causing damage to the head or the debris being carried to newer locations.

This could explain why progressively more bad sectors develop following the initial bad sector. Though a bad sector is marked as such and nothing is written to that sector, a cylinder has something like 63 sectors and while reading other good sectors on that cylinder the head passes over the bad sectors too!

Perhaps I am totally wrong in my deduction but my approach has helped me to use hard disks without any problem of progressive development of more damaged sectors any sooner.

My secret is to prevent the head from accessing the entire cylinder with the damaged sector along with a few adjacent cylinders!

And this is where Mikhail Ranish's wonderful Partition Manager comes in handy (Read about it in the hard disks page). As I have said elsewhere this is a very powerful tool and can cause loss of data in the hands of the uninitiated. However once you understand the working of this piece of software hours of gainful pleasure is assured

First things first

Read the documents that come with Ranish's Partition Manager and familiarize yourself with how it can be used. Actually when you use Ranish's Partition Manager you will never lose your data as nothing is written to the data area or the system area (containing the Directory and File Allocation Tables) by it; modifies only the partition table. When you run Ranish's Partition Manager first time on the disk make a note of the CHS (Cylinder-Head-Sector) values for all the existing partitions so that, if you need, you can key in the values once again to bring the hard disk back to the original condition. Your data is back, unless you tried to write something to the disk in between.

Get yourself a DOS boot disk. If you need to work on large disks you will need a Windows Boot Disk. Ranish's Partition Manager 2.37 will work with partition sizes smaller than 2 GB (DOS limit) and version 2.43 will be required for larger partitions.

Start in earnest

First you will have to identify the cylinders that contain the bad sectors. Ranish's Partition Manager has a surface verification tool that is very fast and comes into play when you press 'V' when you are in any partition (the one highlighted) and verifies all the cylinders in the partition. Let us say that the disk we are looking at has no partition yet. So mark the full disk as a single partition using Ranish's Partition Manager. Press 'V' and the verification dialog box opens and starts counting the cylinders that are ok. Watch carefully because it stops at the first cylinder with a bad sector and note the cylinder number. Let us assume that in our test hard disk this is cylinder number 106 and that the disk has a total 600 cylinders.

Now using Ranish's Partition Manager setup the cylinders 1 to 103 as the primary partition. and cylinders 109 to 600 as the extended partition. Set up the entire extended partition as one logical drive. This effectively eliminates cylinders 104 to 108 both inclusive marking them as unused. The head never ever goes over the defective cylinder 106 but also avoids 2 cylinder either side of it. (Cylinder-Head-Sector structure is a complicated affair and some translation is done by the electronics on the hard disk. In large disks it is safer to eliminate more cylinders either side of the one that has the bad sector)

Repeat verification of the logical drive that starts at cylinder 109 and note down the number of the cylinder that has a bad sector, say 201 in our example. As before create a logical drive spanning cylinders 109 to 198. And a new logical drive starting with cylinder 204. This eliminates cylinders 199 to 203, marking them unused.

Repeat this process and recover as many partitions as you can. There are occasions where a number of adjacent cylinders may have bad sectors. You may have cylinder 206 bad and when start working on the next partition you will find 211 also bad. In these cases eliminate all cylinders between 206 and 211 as well as two or three cylinders either side of them. Otherwise you will be creating partitions that are too small to be of any practical use.

This way you have now removed the possibility of the read head of the hard disk going over or near the damaged sectors and this, in my experience, stops creation of more bad sectors.

Disclaimer

The above is not for people who have no time or inclination to experiment; or adventurous. Nor am I responsible if you lose part or whole of your hard disk in attempting to do what I have done. You have been warned. If you can afford to buy a new hard disk, by all means do it and get going. This page is only for the experimenter like me who derives immense satisfaction using a drive that has developed many bad sectors at different locations by the time I hit on this idea, and only 50 percent of it was usable. After applying the above method of elimination of cylinders I have been using this disk for more than two years now without any new bad sectors and have never lost my data.

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