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Thread: The most reliable way of finding bad blocks on MFM drive?

  1. #1

    Default The most reliable way of finding bad blocks on MFM drive?

    Hello, what is The most reliable way of finding bad blocks on MFM drive?
    I usually use IBM enhanced diagnostic disk for PC XT for low level formatting hard drives on my IBM XT with ST-412 hard drive. This done without fine without finding of any BBs.
    Also high level format did not detect any problems on disk. I recorded some data to this disk and normally used.
    Finally I tried software SPINRITE ver. 4 and level 4 scanning of disk surface. Suddenly program found a lot of BBs. How is this possible? Low level format and also high level format did not find anything.
    Its good way to torture these old disks with level 4 (or 5) of spinrite surface scan?

    Roman.
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  2. #2
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    What model of controller and hard drive are you using? About how many bad sectors did Spinrite find?

    On MFM and RLL hard drives, it is all too common to have "weak" sectors that an initial formatting/testing won't find.

    - It is easier for a controller to read a sector filled with zeros than a sector stuffed with random data.
    - In DOS FORMAT, Bios will usually retry a few times and if a retry eventually succeeds the sector is marked as good.
    - Weak sectors often become harder to read over time, even if they remain empty.

    For example, if you had just formatted the drive, a tool like Norton Disk Test 4.5 might at first show no errors or only a couple of errors detected by FORMAT. Then you copy a large ZIP file in to the drive, after which Norton Disk Test then starts to retry more and detects some bad sectors. Then you wait a few months and try Disk Test again, which now reports a few more bad sectors. This is all unfortunately quite normal, and the drive is not even bad.

    When these drives were new, they relied on users entering the manufacturer's bad track data written on the drive. Most drives by now have developed a few other bad/weak areas although they can still work fine.

    This is why running Spinrite and its pattern test can be important.

    There is a detailed description of how Spinrite works here: https://forum.winworldpc.com/discuss...light-spinrite

    Typically after running Spinrite there should be no or few additional errors found over time. But it is a good idea to periodically follow up with least a quick test using Norton Disk Test or a similar too.

    Just running Spinrite will not damage a drive. However if a drive is already falling apart then the tests could push it to failure, but it would have failed anyway.

  3. #3

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    I am using first generation of IBM/XEBEC disk controller And also standard Seagate ST-412 hard drive

    I dont know exact number of new BBs found by Spinrite, its few, its not terrible anyway.

    Weird is also scanning with "level 5" intensity. Level 5 can return some bad sectors to use. I tried also this and really some BBs disappeared. Wrong side of this is fact, that these BBs returned after some weeks of disk using and was found in next scan.
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155: IBM PC Expansion Unit 5161:
    WANTED!: IBM 5175 monitor, IBM 5145 monitor, IBM PC/XT/AT rear screws, Intel INBOARD 386AT card, IBM 5140 keyboard, very early IBM PC (S/N: under 5000)
    My IBM PC hardware collection

  4. #4
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    I have a drive that does that too. Some of the "weak" sectors only fail or retry a read perhaps one out of every few dozen reads, so Spinrite may try to return them to active use. Unless you have started all over with a controller LLF or changed interleave, then on subsequent Spinrite runs, it is usually a good idea to disable its ability to return sectors to active use.

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    Used to be, that if you wanted a reliable drive that had bad spots, you'd flag the whole track (many controllers have firmware to do just that). Bad spots on a track can have a tendency to "creep" a bit. Better to ignore the track and move on.

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    Seconded. Never return bad sectors/clusters to active use.
    Offering a bounty for:
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  7. #7

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    Quote Originally Posted by Chuck(G) View Post
    Used to be, that if you wanted a reliable drive that had bad spots, you'd flag the whole track (many controllers have firmware to do just that). Bad spots on a track can have a tendency to "creep" a bit. Better to ignore the track and move on.
    I would think after 30 years they've probably creeped as much as they're going to creep, no?

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    What makes you think that? Over time, the disk surface deteriorates; I'd think that if it started out with a defect, things wouldn't improve much.

    Witness the old drives that have developed errors on track 0, which should, in theory, be the best track on the drive.

  9. #9

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    Quote Originally Posted by Chuck(G) View Post
    What makes you think that? Over time, the disk surface deteriorates; I'd think that if it started out with a defect, things wouldn't improve much.

    Witness the old drives that have developed errors on track 0, which should, in theory, be the best track on the drive.
    Fair point.

    The two ST-225s that I've had since back then are still stable, one has 0 bad blocks and the other has 3, but each one is only a single sector on 3 different tracks. Granted my sample size is tiny.

  10. Default

    If you have an old MFM hard disk drive, which was already stressed from years of usage, you might kill it finally by using Spinrite.
    I recommend to make a backup, then low-level format the MFM HDD, and after this, restore the content.
    Spinrite is something I call "Snake oil", but I know there are still so many people who swear this software will generate miracles.
    My own expirience ... used it to test an old PS/2 ESDI drive, and after it, the drive was almost dead. I had a similar case and I just low-level format it (instead of using Spinrite) and all went good.
    My learning... if someone try to sell a "spinrite" tested MFM drive to me, I refused to buy it.
    Remember, there is an expected life span for a MFM drive, and it would be not a good idea to reduce the life span by additionally stressing these old drives.

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