I just noticed that I seem to have an almost duplicate partition of my iMac hard drive.
The 2TB Fusion drive seems to be split down the middle with 'Mac HD' and 'Mac HD - Data' drives
I don't believe that I created this partition
Any thoughts on how this might have happened?
iMac 27″, macOS 10.14
The extra partition is part of the new APFS formatting which you created when upgrading to Mojave. APFS creates four partitions. One is visible, Mac HD. The others should be hidden. These are Mac HD - Data, Preboot, VM, and Recovery. The Data volume contains all the files and folders on the drive that are not part of the bootable OS system files. This system partition is locked to prevent any access by the user. The one visible partition is Mac HD which uses special links to the Data disk's content.
There is nothing wrong with your drive. If the Data partition is visible on the Desktop, you should not be concerned. When you upgrade to Catalina, the Data partition will no longer be visible.
The extra partition is part of the new APFS formatting which you created when upgrading to Mojave. APFS creates four partitions. One is visible, Mac HD. The others should be hidden. These are Mac HD - Data, Preboot, VM, and Recovery. The Data volume contains all the files and folders on the drive that are not part of the bootable OS system files. This system partition is locked to prevent any access by the user. The one visible partition is Mac HD which uses special links to the Data disk's content.
There is nothing wrong with your drive. If the Data partition is visible on the Desktop, you should not be concerned. When you upgrade to Catalina, the Data partition will no longer be visible.
With APFS space is shared. That Other Volumes represents the space allocated in the container. It is correct but confusing. In reality your drive is only about half full. The other half is reserved in the container. The 152GBs of free space is what isn't allocated in the container at this time.
I don't know what it showed because you did not post the information. As I said earlier, there are not two partitions on the drive. There is only one - Container disk2. Two "synthetic" logical volumes - Mac HD and Mac HD - Data - are sharing the total capacity of the drive. In all the information that you posted for me, I did not see anything that appeared to show "duplicated" data in each volume. The Mac HD volume uses special hard links (aliases) to the real data contained on the volume Mac HD - Data. This will appear as if the data were also on Mac HD. The space difference is accounted for by the macOS system files that are not located on Mac HD - Data.
I'm afraid I don't know how to better explain this since I am not a developer or programmer. I'm just a technically oriented person who has used Macs for nearly 30 years.
I guess I was using the term 'partition' incorrectly - I merely meant two separate volumes on the same physical drive.
I was able to delete this synthetic logical volume and merge its capacity back into the 1st volume.
I'm pretty sure that happened is that the Data volume was a remnant of my brief upgrade to Catalina in April.
Thanks for the input and for helping me figure this out
First, do you have Time Machine enabled but no backup drive connected? Second, have you tried booting from the Recovery Volume and running First Aid on the drive?
Open Disk Utility. In the upper left corner is a dropdown menu labeled, "View". From that menu select "Show All Devices." Be sure you see all disks, containers, and volumes. Then take a snapshot of the Disk Utility window and post it in your reply.
Well, all of that looks OK. I guess we go a little deeper. Open the Terminal in the Utilities folder. At the Terminal's prompt enter or paste the following:
diskutil list
Press Return. Select and copy the resulting display from the Terminal's window. Paste it into your next reply. I'm going to get to the bottom of this, if I can.
Thanks. I don't see anything unusual in the image. Please send me two more. One with only Justin's iMac volume selected, and one with only the Data volume selected.
Everything looks A-OK to me. What gets reported in Get Info?
It's showing you an estimate of free space which in Disk Utility is shown as 152GBs. Free space measurements are confusing in Mojave and Catalina due to the use of APFS. The best indicator to rely on is:
Select a Desktop disk icon. Press Command-I to open the Get Info window and look at the topmost panel displayed. You will find the disk information displayed for Capacity, Available, and Used. If you have more than one disk/partition then repeat for each one on your Desktop.
Get Correct Storage Information
To find out the correct information for any disk: Select a Desktop disk icon. Press Command-I to open the Get Info window and look at the topmost panel displayed. You will find the disk information displayed for Capacity, Available, and Used. If you have more than one disk/partition then repeat for each one on your Desktop.
Never believe that graphic bar. Use Finder to tell you how much free space you have. The Graphic bar is notorious for being in-accurate. To see in Finder please do the following:
I just booted into Recovery Mode and ran First Aid on both partitions - Justin's iMac seemed OK but the Data drive reported 'snapshot fsroot tree corruptions' that'll 'go away once the snapshot is deleted'
Here you go, thanks
Justins-iMac:~ jsurpless$ diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *2.0 TB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk2 2.0 TB disk0s2
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *121.3 GB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_APFS Container disk2 121.1 GB disk1s2
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +2.1 TB disk2
Physical Stores disk1s2, disk0s2
1: APFS Volume Justin's iMac - Data 999.7 GB disk2s1
2: APFS Volume Preboot 42.3 MB disk2s2
3: APFS Volume Recovery 510.5 MB disk2s3
4: APFS Volume VM 2.2 GB disk2s4
5: APFS Volume Justin's iMac 957.5 GB disk2s5
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk3
1: EFI EFI 209.7 MB disk3s1
2: Apple_HFS Justin's Backup 3.0 TB disk3s2
/dev/disk4 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk4
1: EFI EFI 209.7 MB disk4s1
2: Apple_HFS Safe Backup 3.0 TB disk4s2
OK, that is interesting - I must have missed that mention when upgrading to Mojave
What has me still confused is that I am being told that I only have ~150GB free out of 2TB
I don't have 1.8TB of data on the drive
****EDIT****
Could this have been caused by my temporary upgrade to Catalina? I did it for a few hours only to decide that I wasn't happy with the loss of certain apps vs the new feature set. I restored via a TM backup from prior to the upgrade
As an aside, the graphic bar is accurate but confusing. It represents space shared in the container. The "Other" is shared space used by another volume in the container. I think that is confusing enough, eh?
Why Do I Have An Almost Duplicate Partition?
