How do you resize an external drive partition with Disk Utility on Catalina?

[Awoodworkerslife]

Hi all,
Last month I upgraded my 2017 MBA SSD from the stock 250 GB to a 1 TB SSD, and now I'm getting notices that time machine backups are failing because I don't have enough space on my external drives. They are 3TB drives partitioned into 500GB for Time Machine and 2.5TB for my photography business (I'm only using 1 TB of the available 2.5 TB in the photo business partition). I would like to change the size of my partitions to 1 TB for Time Machine and 2 TB for the photo business.

It seems to me that this used to be doable using Disk Utility without having to completely erase the external drive, but for the life of me I can't figure it out with Catalina and google isn't being much help either. Any ideas?

 

[MacManiac76]

Is the drive formatted as APFS or MacOS Extended Journaled? Also make sure Show All Devices is selected in the View menu and select the drive name itself, not the partition name to the left in Disk Utility. The Partition button should not be grayed out then so you can try to adjust them. If some of the data cannot be moved to allow for the change, then Disk Utility will not let you do the adjustment.

 

[IowaLynn]

Rule of thumb make time machine 3.5x capacity of files to be backed up. 500 was fine for 150GB in the past.

if you are going to be using 600GB then 2TB would make more sense.

keep 3 sets, two backup sets. So even a failed backup isn’t catastrophic. Various raid arrays can be useful such as RAID5 for your business

Samsung 2TB and then one or preferably two clone style backups that you can work from and boot from.

 

[Awoodworkerslife]

MacManiac76, It's Extended Journaled. I didn't have show all devices selected, thank you for that! Also, I've discovered that I can get the slider buttons on the pie chart to show up by holding down the command button. However, all it will let me do is add an additional partition. I can't seem to increase the actual size of the Time Machine partition.

IowaLynn, thanks, I'll take that into account.

 

[MacManiac76]

There is probably unmovable data on the photo partition. Other than reformatting and partitioning the drive all over again, you could try to move your photos to another drive, delete the photo partition, resize the Time Machine partition, and then recreate the photo partition at the new size. Finally move all your photos back to the newly resized photo partition at the end..If Disk Utility will allow you to do all of this of course.

 

[Awoodworkerslife]

There is probably unmovable data on the photo partition. Other than reformatting and partitioning the drive all over again, you could try to move your photos to another drive, delete the photo partition, resize the Time Machine partition, and then recreate the photo partition at the new size. Finally move all your photos back to the newly resized photo partition at the end..If Disk Utility will allow you to do all of this of course.

OK, thank you. I guess then for what it's worth, I may as well just reformat. I keep 3 physically separate copies of everything so all I really have to lose is the time involved. Thanks for clearing those things up, at least now I know I'm not missing something with regards to not finding a resize function in Disk Utility.

 

[Riwam]

There are tools like Stellar Drive Manager which say they can resize volumes without Data Loss but it did not work for me when I tried it. The advice of MacManiac76 seems entirely reasonable. One can never be too cautious in order to avoid Data Loss
Never try anything unknown without previously making back ups and checking that they actually work. If for instance you make a clone of a volume for additional safety, check that you can actually boot from that clone before undertaking any risky change and resizing any partition is indeed risky.