Welcome, Guest
Username: Password: Remember me

Search Micromat Forum

Keyword

TOPIC: Stuck on Prechecking Structures

Stuck on Prechecking Structures 21 Mar 2019 20:55 #10901

I have a roll-your-own Fusion drive on a 2008 iMac that won't finish booting (even in Single User mode). The Fusion drive passes Volume Structures, and each physical drive passes Partition Map, SMART, and Surface Scan. But the drive won't mount, and Volume Rebuild gets stuck forever (more than a day) on Prechecking Structures.

Is there anything else I can do to try to save this drive, or am I stuck with reformating and restoring?
The administrator has disabled public write access.

Stuck on Prechecking Structures 21 Mar 2019 21:14 #10902

TechTool Pro 10 can get stuck at Checking Prestructures if you run it under Mojave, but unless you have hacked the computer you are not running Mojave.

Thanks for making clear what tests you ran.

It would be interesting to see what Disk Utility does.

There is probably something wrong with the whole Core Storage setup, so reformatting, and restoring is the only option. If I were in your situation, I would see if there are any online tutorials for making a "roll-your-own" Fusion drive that have instructions that differ from the ones you originally used, and claim to be better in some respect.
MicroMat Inc
Makers of TechTool
The administrator has disabled public write access.

Stuck on Prechecking Structures 22 Mar 2019 00:53 #10905

I'm running macOS 10.11.1 on the eDrive.

Disk Utility 15 just shows "Loading disks" forever, but a copy of Disk Utility 13 hacked to run under El Capitan shows no errors when verifying the Fusion drive, but encounters an error when trying to mount it.

You may be right about the method I used having issues, but it had no problems for years, until now.
The administrator has disabled public write access.

Stuck on Prechecking Structures 22 Mar 2019 01:22 #10906

Thanks for reporting the results of using Disk Utility.

I hope you will have better results with your next "roll your own" Fusion drive.
MicroMat Inc
Makers of TechTool
The administrator has disabled public write access.

Stuck on Prechecking Structures 23 Mar 2019 00:30 #10907

So part of the problem here might be that the disk won't unmount. It's not actually mounted, but the diskutil command reports that it could not be unmounted, and there's a folder with the "no access" icon on it in /Volumes with the name of the Fusion drive. Any tips on getting it to fully unmount? At this point I can't even erase it.
The administrator has disabled public write access.

Stuck on Prechecking Structures 23 Mar 2019 01:39 #10908

Here is an earlier thread on trying to unmount a volume

Stalled trying to unmount Fusion Drive

There is one thing you could check using Terminal. It will not repair anything, but it will at least make it possible to see if the partition map can be read. I do not have a Fusion drive, and I do not know just how the rotational part and the SSD part appear in Diskutil. I assume you know how to find the BSD identifiers for volumes, using diskutil list:

Macintosh:/ MMT3$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            4.0 TB     disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

/dev/disk1 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        +24.3 MB    disk1
   1:        Apple_partition_map                         32.3 KB    disk1s1
   2:                  Apple_HFS Flash Player            24.2 MB    disk1s2

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Super_Duper_Clone       477.1 GB   disk2s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3
   4:                  Apple_HFS eDrive                  21.9 GB    disk2s4

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS H_G_Wells               4.0 TB     disk3s2

Macintosh:/ MMT3$


After you find the right identifier , try this command. In this example, the identifier is disk0:

Macintosh:/ MMT3$ cd /
Macintosh:/ MMT3$ sudo gpt -r show disk0
Password:
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640  7812357952      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  7812767592     1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  7814037128           7         
  7814037135          32         Sec GPT table
  7814037167           1         Sec GPT header
Macintosh:/ MMT3$

I do not have any experience with making Fusion drives myself. I just think it is useful to know if the partition map can be read. If it cannot be read, it is possible that part of it resided on blocks that went bad, and got remapped to spare, empty blocks. Such blocks, already remapped, will not show up as errors in the Surface Scan.
MicroMat Inc
Makers of TechTool
Last Edit: 23 Mar 2019 01:41 by micromattech3.
The administrator has disabled public write access.

Stuck on Prechecking Structures 23 Mar 2019 01:54 #10909

I have seen cases in which diskutil, Disk Utility, and any other program that addresses drives directly do not work properly because some diskutil code is corrupted in RAM. In one case, Disk Utility was misidentifying volume formats. The only solution was a shutdown, turning off all external drives, waiting a while, and rebooting.
MicroMat Inc
Makers of TechTool
The administrator has disabled public write access.
Time to create page: 0.365 seconds