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TOPIC: I/O and CRC Errors

I/O and CRC Errors 09 May 2019 16:38 #11048

TTP is reporting I/O errors on a regular basis. However, when I search Console for "I/O” (or “i/o”), I get no results. However, Drive Scope is showing that the drive (actually one of two in a roll-your-own Fusion drive) has a CRC error count of 227,281.

But the drive passes all tests! Volume structures, surface scan, Drive Scope extended offline self-test, everything.

I’m worried that this drive is failing—my computer has certainly been behaving oddly. But is it? Or is it the sled? Or perhaps even the other drive in the Fusion drive (which has an ATA error count of 16, but also passes all tests)? Is there a way to know without swapping out drives to find out?
Last Edit: 09 May 2019 17:32 by Calion. Reason: link format
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I/O and CRC Errors 09 May 2019 17:27 #11050

You should be able to distinguish drive mechanisms in Drive Scope. I do not have a Fusion Drive, so if you need help with that, please send a message to This email address is being protected from spambots. You need JavaScript enabled to view it. . Thank you.

The aspects of the drive measured by SMART testing have little overlap with the other tests in TechTool Pro. Even if the Volume Structures test and the Surface scan have a result of Pass, the SMART test can show failures.

The CRC error count suggests that something is wrong with the drive, the port to which it is connected, or the cable.

From Wikipedia's SMART Test article:

The count of errors in data transfer via the interface cable as determined by ICRC (Interface Cyclic Redundancy Check).
MicroMat Inc
Makers of TechTool
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I/O and CRC Errors 09 May 2019 17:31 #11052

micromattech3 wrote:
You should be able to distinguish drive mechanisms in Drive Scope.

Yes, absolutely. That’s why I know that the SSD is getting CRC errors, and the HDD is getting (a few) ATA errors.
The aspects of the drive measured by SMART testing have little overlap with the other tests in TechTool Pro. Even if the Volume Structures test and the Surface scan have a result of Pass, the SMART test can show failures.

But it doesn’t. It passes all tests in Drive Scope. That’s what’s confusing. The SSD is under warranty, so if it’s bad, it’s an easy fix. I just want to know how to figure that out.
The CRC error count suggests that something is wrong with the drive, the port to which it is connected, or the cable.
Thanks, that’s helpful.

I’ve read in another thread on here that I/O errors are from the System.log, but I can’t seem to find them. Help?
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I/O and CRC Errors 09 May 2019 17:37 #11053

You are welcome.

You should report the CRC error count to the maker of the drive.

The location of some of the error messages has been changed, and these messages are not as easy to find as they were before. Please send a message to This email address is being protected from spambots. You need JavaScript enabled to view it. , including the macOS version you are using, and ask where the i/o errors reported by TechTool Pro should appear. Thank you.
MicroMat Inc
Makers of TechTool
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I/O and CRC Errors 09 May 2019 17:39 #11056

Thanks again. By the way, this is in El Capitan.
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I/O and CRC Errors 09 May 2019 17:42 #11057

There should not be a problem with using either program with El Capitan.
MicroMat Inc
Makers of TechTool
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I/O and CRC Errors 09 May 2019 18:22 #11060

Please take a look at page 35 of the Drive Scope manual (page 40 of 54 of the pdf file):

www.micromat.com/product_manuals/drive_scope_manual_01.pdf
MicroMat Inc
Makers of TechTool
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