[solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

user21767638931 · 2016-12-31 00:36:53

Hi, I am trying to install Arch (dual boot) on my early 2015 rMBP 12,1, and am having trouble partitioning the disk. I just did a fresh restoration of OSX Yosemite, updated firmware, and have created only one new partition with Disk Utility for Arch, which is half the size of my disk, saving the other half for OSX. (125G each).

I am mostly confused about the status of disks /dev/sda vs /dev/sdb, and why I have /dev/sda showing up as 28G size? Here is the output of a few commands to try and illustrate my situation:

fdisk -l :

Disk /dev/sda: 28.9 GiB, 30970740736 bytes, 60489728 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x4032ce55
 
Device          Boot     Start             End       Sectors      Size      Id     Type
/dev/sda1      *           0           1636351      1636352     799M      0      Empty
/dev/sda2                 172          82091        81920       40M      ef     EFI (FAT-12/16/32)

Disk /dev/sdb: 233.8 GiB, 251000193024 bytes, 490234752 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 6A160358-DB30-4B85-BC43-33F72B3FE853
 
Device             Start          End         Sectors     Size      Type
/dev/sdb1         40           409639        409600        200M     EFI System
/dev/sdb2         409640     245412519     245002880     116.8M     Apple Core storage
/dev/sdb3         245412520   246682055      1269536     619.9M     Apple boot
/dev/sdb4         246682056   489972567     243290512     116G     Apple HFS/HFS+

Disk /dev/loop: 348.7 MiB, 365662208 bytes, 714184 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

sgdisk -v /dev/sda :

********************************************************************************
Found invalid GPT and valid MBR: converting MBR to GPT format
in memory.
********************************************************************************

No problems found. 60407741 free sectors (28.8 GiB) available in 2
segments, the largest of which is 60407603 (28.8 GiB) in size.

sgdisk -v /dev/sdb :

No problems found. 262157 free sectors (128.0 MiB) available in 2
segments, the largest of which is 262151 (128.0 MiB) in size.

And when I run "cgdisk /dev/sda" it displays this warning:

Warning! Non-GPT or damaged disk detected! This program will attempt to
convert to GPT form or repair damage to GPT data structures, but may not
suceed. Use gdisk or another disk repair tool if you have a damaged GPT disk.

Press any key to continue......

pressing a key to continue, cgdisk displays the following for /dev/sda:

Part. #    Size    Partition Type     Partition Name
-------------------------------------------------------------------
      69.0KiB    free space
2    40.0 MiB   EFI System     EFI System
      28.8 GiB    free space

quitting cgdisk, and running "cgdisk /dev/sdb" instead, shows the following:

Part. #    Size    Partition Type     Partition Name
-------------------------------------------------------------------
      3.0KiB    free space
1    200.0 MiB   EFI System          EFI System Partition
2    116.8 GiB    Apple Core Storage    Macintosh HD
3    619.9 MiB    Recovery HD          Recovery HD
4    116.0 GiB    Apple HFS/HFS+          Macintosh HD 2
      128.0 GiB    free space

As I have just erased my OSX and reinstalled, I am quite lost in terms of why my disk are in such a state. From the information above, should I be using cgdisk to partition dev/sda or /dev/sdb for the arch installation? I am confused as all information I find says to use /dev/sda, and I am just a beginner so I am not sure how to properly troubleshoot my issue. Thanks very much in advance for any help!

Last edited by user21767638931 (2017-01-02 07:38:34)

Docbroke · 2016-12-31 03:02:29

It appears that your are having 2 disks in your system with /dev/sda is used as boot partition (probably SSD) which has unused 28GB space free, while system is installed on /dev/sdb ( the one which you have partitioned to two for arch and mac installs)
Now for dual boot system I would recommand you continue in the same manner,(install arch in /dev/sdb2 or /dev/sdb4) while keeping /dev/sda as /EFI partition. One more thing is 40 MB is little less if you want to use two or more OSes, I would suggest you to increase it to 512MB or atleast 256MB, otherwise you may get issues with bootloader installation.
You may even have arch installed on current free space in /dev/sda, with your home partition on /dev/sdb

R00KIE · 2016-12-31 15:59:32

If I had to guess I'd say that 28GiB disk is the flash drive or whatever you are using to boot and the 233GiB disk is the internal disk.

user21767638931 · 2016-12-31 22:55:00

Thank you both for your answers. @R00KIE - you were correct! I tried creating a bootable USB with another stick of different size, and things have now reversed, (system showing up on /dev/sda and /dev/sdb is now 16GiB).

What can I say, first timer over here. Thanks again.

Docbroke · 2017-01-01 11:34:42

kindly mark this thread as solved if your issue is solved by prepending [solved] to the title, by editing your first post.

Arch Linux

#1 2016-12-31 00:36:53

[solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

#2 2016-12-31 03:02:29

Re: [solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

#3 2016-12-31 15:59:32

Re: [solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

#4 2016-12-31 22:55:00

Re: [solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

#5 2017-01-01 11:34:42

Re: [solved] cgdisk - Warning! Non-GPT or damaged disk detected! ...

Board footer