Open Radar

 
Summary:
Some external hard drives, such as the 4TB Seagate Expansion Desk Drive will result in kernel messages such as "alignment error":

10/5/15 6:13:14.000 PM kernel[0]: disk3s3: alignment error.

Steps to Reproduce:
1. Find a 4K drive, such as a Seagate 4TB Expansion Drive [model SRD00F2] and attach to an El Capitan System

Expected Results:
I expect the external hard drive to work flawlessly on OS X 10.11 just like it did on 10.10, 10.9, and 10.8 before that.

Actual Results:
OS X complains about disk alignment errors but provides not insight into why or what specifically the problem is. Is the issue physical block size alignment? Is it logical block size? Is it allocation size? The error message is useless.

Additionally, considering that the disk was formatted with both diskutil and Disk Utility.app with the same results, there should be no errors whatsoever.

Finally, the same alignment errors do not appear on any previous version of OS X. The alignment errors are reproducible on two external hard drives on two different Macs with the same results. The same hard drives work flawlessly in an OS X 10.9 virtual machine.

Version:
10.11 (15A284)

Notes:
Possibly related to 4k. However, if that is indeed the case this is a serious regression from the past several OS X releases. A 1TB Seagate drive that I have does _not_ reproduce the alignment errors on El Capitan. The only noticeable difference that I see is that that drive uses a device block size of 512 Bytes as opposed to the 4TB device block size of 4096 Bytes.

Configuration:


Attachments:
'diskutil terminal.rtf' was successfully uploaded.