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I bought a 3.5-inch Toshiba HDWQ140 server class (N300) 4 TB drive on Amazon. I followed instructions to put it into service as the primary storage disk in my 6-year-old TiVo Bolt DVR.

I succeeded in formatting and configuring it using some TiVo-specific, 3rd-party software (centered around MSFtools). All is working as expected, now with greatly increased storage capacity.

One of the last things I did was to wave a strong magnet over the top of the drive mechanism. Believe me, I didn't plan to do this. I was using a strong magnetic-base flashlight near the TV and almost attached the flashlight onto the HDA. It didn't "click" onto the drive, but I felt the strong pull of the magnet toward the mechanism (the cover is stainless, I believe, so the pull wasn't toward that), and pulled away just in time—I hope. My hand, holding the flashlight, didn't stop, it just passed over the drive, almost being pulled onto the HDA.

I put the drive into the TiVo and so far, the TiVo hasn't flinched. All seems OK. But I think any damage depends on how storage is arranged. If the servo information is on the top platter, I think I'm safe, because if the magnet damaged this surface the drive would be dead now, or showing symptoms. If data is written (I presume this is true) in successive cylinders (the innermost tracks constitute cylinder 0; the next tracks are cylinder 1; then cylinder 2, etc.), then any damage to the top platter would affect all cylinders, and therefor all data. I think I'd be seeing some symptoms by now.

If my understanding of data storage is correct, any anomaly caused by my magnet would show up immediately, because all data is written to successive cylinders on all platters. I think I would have damaged all data on the drive.

I pulled out the drive from the TiVo and did a read-only badblocks scan; it took 6 hours and found no errors:

badblocks -vs /dev/hdb

Less than 5% of the drive's capacity is being used presently.

Do you think I’m safe? Would you place the drive in service or replace it?

Thanks.

EDIT: I replaced the small, mealy magnets on this flashlight with one of these. It's strong:

https://www.amazon.com/s?k=ASIN+B074BP1FR8&i=industrial&ref=nb_sb_noss

iXod
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    If badblocks shows it as fine, it is probably fine. – Zoredache Jul 08 '21 at 21:43
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    Does https://superuser.com/questions/568336/what-is-the-tolerable-magnetic-field-in-tesla-for-a-hard-disk answer your question? – u1686_grawity Jul 08 '21 at 22:21
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    You don't have a magnet strong enough to damage the drive. – Moab Jul 08 '21 at 22:47
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    You can alleviate your concerns by simply reading *each and every* LBA (in use on the drive) with the SMART extended (aka long) self-test. See https://superuser.com/questions/693003/badblocks-vs-smart-extended-self-test BTW *"the innermost tracks constitute cylinder 0"* is backwards. See https://superuser.com/questions/643013/are-partitions-to-the-inner-outer-edge-significantly-faster/643634#643634 – sawdust Jul 08 '21 at 23:50
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    The *very* strong pull is likely due to the positioning system in the HDD, which uses powerful rare-earth magnets and a "voice coil" to move the read/write heads rapidly and precisely. The attraction to the microns-thick magnetic coating was negligible, and spread across all the platters. You didn't damage those magnets, but if you ever discard a hard disk, the magnets are worth saving. – DrMoishe Pippik Jul 09 '21 at 00:49

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(OP) Thanks to all who responded. Great bunch of knowledgeable folks here.

I'm accepting DrMoishe Pippik's answer as the one that made up my mind: it wasn't the platters' magnetic material that attracted the magnet so strongly, but rather the head-positioning magnet. That's a relief to know.

I'll put this drive back in service.

Cheers.

iXod
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  • The usual way to get a comment converted to an answer (which you can then accept) is to ask the commenter to write it as an answer. – Andrew Morton Jul 09 '21 at 15:52