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Question: EMI Shielding for IDE cables

Discussion in 'Electronic Basics' started by blue, Aug 19, 2004.

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  1. blue

    blue Guest

    (Long story)
    I am having problems with hard drive data corruption.
    I have recently rebuilt some of my computers in rackmount casings. After
    running them for a few weeks, I noticed that all of my files were becoming
    corrupted. I have 4 x 160GB + 4 x 120GB hard drives where this is becoming a
    problem. 2 of the drives lost their partition tables and became completely
    I made valiant efforts to recover and preserve my data, but I have basically
    given up.

    After much investigation, I suspect the cause for these problems to be
    related to my IDE cables.
    1. With the chassis layout, the power supply is located at the front of the
    case, leaving an AC power cable running directly under the hard drive bays
    and the ide cables.
    2. The rack itself houses 6 computers, 2 UPS, 2 power bars, and about 10-15
    other devices (modems, switches, etc), so I expect that there is quite a bit
    of interference here.
    3. I am using flat ribbon 24" and 36" IDE cables, because shorter cables
    will not reach from the drive bays to the ide controller connectors.
    4. All drives are running ATA100

    When doing data recovery, I removed the drives from the cages and ran short,
    <18" ribbon cables. This seemed to greatly reduce the incidence of new data

    I have recovered whatever I could from the drives. They are now all freshly
    formatted and repartitioned. Because of the problems I have had, I am afraid
    to use them for anything.

    I truly do believe that the IDE cables are my problem. I ordered a bunch of
    rounded 36" ide cables, but when I got them, I realized they have no
    shielding at all (I thought the point of rounding a cable was to put a
    shielding around it!).

    I expect that shielding these cables may help fix my problems. I am looking
    for any advice on doing this. I initially thought I'd just get some aluminum
    muffler tape from the auto parts store, and wrap the cables, but I'm not too
    - Do I need to put a ground wire onto the shield? I think it would make
    sense to have a drain on one end of the shield and attach it to the chassis
    - Should I put one of those ferrite clamp shields on the ide cables?
    - Should I put one of those ferrite clamp shields on the internal AC power

    I also think it would be smart to wrap any shielding in an insulating
    material, like electrical tape or something. But when electrical tape heats
    up, the adhesive makes everything gooey. I don't know if I can fit heat
    shrink tubing over the connectors. Any other ideas?

    Thanks for making it to the end of this long email!
    creekchubbAThotmailDOTcom (replace AT with @, and DOT with .)
  2. Kevin Kilzer

    Kevin Kilzer Guest

    It is unlikely that shielding is the culprit, and more likely that
    grounding or other power supply issues is the problem.

    By reducing the cable length, you have actually reduced the need for
    good grounding. The suggestion by tempus fugit that 80-pin cables is
    right-on, since those cables are required for proper ATA100 operation.
    They provide 40 additional ground wires in each cable (which is not
    quite the same as shielding). Standard ATA cables have only 5 or 6
    ground conductors.

    You should also check the quality of the cabling in the power
    connections. If you changed cases, I assume you also changed power
    supplies and likewise the distibution of power. Watch out for those
    "Y" cables in the power supply -- the standard ATA power connector is
    notorious for getting bent out of shape if they are plugged/unplugged
    a number of times.

  3. tempus fugit

    tempus fugit Guest

    I think the 80 connector (but still 40 pin) IDE cables are already shielded,
    arent they (that's the extra 40 connectors)?
  4. Spajky

    Spajky Guest

    they are not "shielded", just the extra wires going between signaling
    ones are "grounded" to minimize crosstalk in signal wires ...
  5. blue

    blue Guest

    Thanks for the replies,
    I am using new aftermarket power supplies (thermaltake 480W). I've dealt
    with power supply problems with hard drives (long ago in the past), and the
    symptoms don't fit my current situation. Drives are always detected in bios,
    drives always spin up properly, drives are always accessible through os.

    The reason why I think it is interference of some sort:
    I did some checking of a bunch of corrupt files in a hex editor. I actually
    had chunks of text from other text files. So data got scrambled up during
    read/writes to the drives.
    Switching to a shorter cable to do data recovery also meant unscrewing the
    drive from the bay, and just sitting it in the chassis next to the ide
    controller plug. This moved the drive away from the power cabling. Also,
    when doing recovery, I removed the rack chassis from the rack. With this
    done, I did some file copying tests to see if I was still getting
    corruption, and I did not. The same tests, with long ide cables, and the
    drive mounted in the bay, gave corruption errors. Test file was a large rar
    archive set, test was a sfv file check.
    I am using flat ribbon IDE cables, 80 conductor / 40 pin. I understand that
    the second connector is a ground, which should eliminate cable crosstalk.
    But I do believe that my problem is actual RF or EMI interference.
    I need to use longer cables because of the chassis layout - 24" - 36". It
    would seem to be quite easy to shield the rounded cables from EMI with some
    aluminum tape, I just don't really know what I need to consider. An EMI
    shield doesn't really make sense to me without a ground. And, is aluminum
    muffler tape the right stuff to use?

    I am definitey paranoid of data corruption now - the amount of data I lost
    was crazy. I could have never imagined losing a full terabyte of data all at

    creekchubbAThotmailDOTcom (replace AT with @, and DOT with .)
  6. Rich Grise

    Rich Grise Guest

    It would certainly work, as long as you're sure that you make a good
    connection to it. You can't solder aluminum, you know - I'd seriously look
    into some kind of contact that's designed to connect aluminum to copper.

    And only ground it at one end.

    It would also probably help to see to it that it's not a spiral-wound
    inductor - be sure that there's contact from one strip to the next.

    Or, get really wide aluminum tape and attach it lengthwise.

    Good Luck!
  7. dude

    dude Guest

    Bad shielding could cause data transfer errors but could it really cause the
    loss of the partition table? Assuming you are using FAT32 or something
    similar I could see the FAT getting corrupted but the partition table? That
    would require writes to sectors that shouldn't normally be written to.

    are you sure something isn't erasing the drives themselves? like very strong
    interference hitting the drives from the power supply?

    Also, couldn't you put those round metal rings around the power cables to
    stop some of the interference? not sure how much those help???

  8. tempus fugit

    tempus fugit Guest

    It would be better to ground it, of course, but you would still get some
    shielding from just wrapping it in the tape.
  9. blue

    blue Guest

    Thanks all for the replies.
    Thanks for the thought on soldering to aluminum tape. I might take a look
    for tinned copper shielding tape. I used some a long time ago when putting a
    booster inside a guitar. Hope it isn't too expensive!
    The power supply is right next to my boot drive, which never had any
    problems with corruption (short cable?). My data drives are relatively far
    away from the power supply. I think I will definitely look for some of the
    ferrite RF shields for the AC cable running through the case. Any idea where
    on the cable to put these?
    More of my story (for those interested in the drama!)
    The drives were big ntfs partitions, some were in raid 0 arrays (2x array of
    [2x120gb]), some as single drives (4x [160gb]) . I think the data was
    degrading due to cable loss over time, but i didn't realize it. Eventually,
    the index tables got messed up, and I started losing directories. This
    caused immediate panic, as I thought one of the drives was going in the
    array, so I started moving data to my 160gb drives. Not much thought to it -
    I've had tons of hard drive failures (dropped heads, bad spindle motors, all
    the common stuff) and my first impulse is to get all the data off. Windows
    chkdsk started coming up on bootup, and made an attempt at 'repairing' the
    faulty tables. (This is now the most destructive thing i've ever seen. I now
    believe chkdsk to be the ultimate 'virtual shredder' program.) What I didn't
    realize was that chkdsk was also destroying my second array. After chkdsk
    was done, the majority of the files on both arrays had disappeared, or were
    in found.### directories, and completely corrupted.
    That's ok, because I had just backed up to the 160gb drives, right? Not
    exactly. Every file that I had copied from the array was corrupted. And
    after checking things out, other files on the 160gb drives were also
    I don't know if the original files were all corrupted (unlikely), or if the
    faulty index tables corrupted the copies (maybe), or if the data was
    corrupted during cable transfer (i believe), or all of the above (probable).
    I switched the 160gb drives to short cables, out of the bays, by accident
    really. I took the drive out, then I reconsidered and wanted to make a last
    ditch attempt at the data. Being lazy, I didn't feel like unscrewing the
    drive cage again, so i just grabbed a short ide cable and set the drive down
    in the case. Suddenly, some of the files that were coming up as corrupt
    earlier, were fine! (blank clueless stare - i must have sat there for an
    hour just staring, no mental activity, would you like fries with that?)
    Got about 30% of my data back, but none of the stuff from the drive arrays
    was recovered.

    So, being paranoid now, I check out another computer - same case, cables,
    and a pair of 160gb drives. Sure enough, I've got data corruption here too.
    I pulled the drives, attached them with a short cable, and was able to get
    most of this data off.

    And now, ultra paranoia. I have a terabyte of blank data drives, and I'm
    afraid to put anything on them. All drives were checked with manufacturer
    utility, and are fine (western digital, by the way, drives are 6-12 months
    old). I'm still testing files for data corruption - all files were copied to
    a pile of 40 & 60 gb drives - and burning off whatever I can to dvd. When
    I'm done with this, I'll be shielding these rounded cables, and figuring out
    how to test the drive setup.

    Thanks for making it to the end!
    creekchubbAThotmailDOTcom (replace AT with @, and DOT with .)
  10. Bob Masta

    Bob Masta Guest

    The fact that you are seeing chunks of text from *other* files
    indicates that the FAT is screwed up. If your problem was
    transmission errors which somehow made it past the error correction
    stuff (which I think is not too likely, but possible), then you would
    have erroneous data in the file you sent. Most likely it would just
    look like garbage, or random byte replacements. I can't see any
    way that it could be parts of other files, barring some otherworldly
    interaction between parallel cables on 2 drives during simultaneous
    writes. Not likely!

    Of course, the FAT on the drive is also written by the same process
    that writes the rest of the file. So it's *possible* that some kind
    of noise pickup could corrupt the FAT data as it was updated. There
    are 2 copies of the FAT, so if they both are identical I'd say that
    was proof the trouble was somewhere else, in software. If it was
    noise in transmission, they would be different.

    If your drives use something other than FAT, like NTFS, then
    the same reasoning applies. But I don't know if or where they
    maintain a 2nd copy.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  11. blue

    blue Guest

    Actually seeing a chunk of recognizable data was a very rare occasion.
    Here's how i found the chunk of text. I renamed some large directories of
    archives, giving all the extension *.txt. I did a search on these files for
    a specific string (my email address). I went to sleep, and the next day, the
    search had found a file. I opened this in a hex editor, and sure enough,
    there was my email address with a small chunk of text from an ancient email
    in there. There is absolutely no reason why a solid data archive should have
    this string, but it did happen, in one file of many.
    This occured once, late in the game, after chkdsk had rewritten my index
    files, so i'm not sure if this had anything to do with it. I did make
    attempts to recover the ntfs index. I mirrored the entire drive with ghost,
    and ran a recovery program from a boot disk. I got nothing useful from this
    except more chkdsk madness on reboot after recovery. I think that a
    scrambled up file index would have the off chance probablilty of referencing
    incorrect data sectors for a file.
    I only did this search once, on files that had been verified as corrupt. It
    was out of curiosity (or madness) only, and didn't really have any purpose.

    creekchubbAThotmailDOTcom (replace AT with @, and DOT with .)
  12. Rich Grise

    Rich Grise Guest

    Duh. Copper tape. Of course! :)
    Just one per cable, near one of the connectors. That's called a common-mode
    choke; a google search should turn something up.
    Everything is pointing at the long cables here. There's a chance that the
    length of the cables itself is the culprit, in which case shielding won't
    help, or could make it worse. If it's easer to try that than redesigning
    the mounting of the drives so you could use shorter cables, then try it
    and see how well it works - I'm sure you could come up with some data
    torture tests. ;-)

    But if it were me, I'd make every possible effort to shorten the cables.

    I know, I'm the one who suggested shielding, but that doesn't help
    with stuff like rise times and transmission line effects and stuff like
    that. At 133 MHz, 3 ft. is starting to approach a significant fraction
    of a wavelength, so impedance matching might be an issue.

    I thought a RAID array was supposed to _increase_ data storage
    reliability? ;-)

    Good Luck!
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