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TOPIC: Bad Blocks Reported

Bad Blocks Reported 20 Sep 2020 23:38 #12396

Recently I have been having issues with an encrypted Time Machine drive so I did a simple wipe via Disk Utility. Then I ran the Surface Scan via TechTool Pro 13 and found over 270 bad blocks on a 300 TB hd.

I didn't let it finish because I've seen enough to know that there's a problem.

And since both "hard" and "soft" bad sectors are possible I zeroed out the drive and have been running Surface Scan via TTP 13 for a day and a half now.

So far, it has completed over a billion (out of almost 6 – 5,860,533,167) blocks, and has yet to find a single bad one. It's also worth mentioning that a lot appeared in clusters in the 3 million, 975 million and 4 billion block areas, for example.

So far, none have reoccured.

I'm still leery though. Do you suggest I run it again when it finishes? And do you also think I shouldn't encrypt it if it turns out okay (because Time Machine's encryption could be causing problems)?

That's just a theory about Time Machine, though I don't want to rule it out.
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Bad Blocks Reported 21 Sep 2020 00:29 #12397

Thanks for your clear and detailed report.

What drive has a capacity of 300 TB?

I think you should let the Surface Scan run to completion. The 270 blocks that could not be read may have been "pending" sectors, sectors that were flagged by the drive because they were involved in some attempt to write that failed.

The Surface Scan in TechTool Pro 12 allows you to choose an approximate starting block, so you could check the areas in which bad blocks were found before.

The SMART test in TechTool Pro shows the current pending sector count, at attribute 197.

Sectors involved in a read/write event may be flagged as "pending" if the drive or the computer suddently loses power. It may be that "pending" sectors cannot be read by the Surface Scan, because the firmware of the drive will not allow any reading or writing at those sectors until the drive itself examines them and either removes the pending flag if they can be read, or remaps them to spare blocks if they cannot.

I do not think that the encryption is related to the results you got from the Surface Scan. The test is checking to see if a block can be read. It does not matter to the test whether the data is correct or not. So, while there could be a problem with the way encryption is working on Time Machine, the Surface Scan would not be affected by that.
MicroMat Inc
Makers of TechTool
Last Edit: 21 Sep 2020 00:41 by micromattech3.
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