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Resizing Partitions
#57925 02/15/21 11:20 PM
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Excuse me if this is not the correct forum, but it seems an application would be needed to re-size partitions. So, here goes.

I understand that Disk Utility (DU), especially for recent versions of the Mac OS (Catalina and Big Sur), is the only reliable program that can be used for re-sizing partitions. But a couple of years ago, I had issues in trying to do that task. And in reading about using DU just a little while ago, it seems to indicate that to resize a partition, the "next" one needs to be deleted first. That seems counter-intuitive, at least for my situation.

I have 2 external Samsung 850 Pro 512 gig SSDs. For both of them, there are 3 partitions: 2 of the partitions, each 100 Gig in Size and formatted as APFS, are used for the SuperDuper! backups for each of my Catalina-based Macs. One of them, the third partition, also formatted as APFS, contains various files, and is a little over 300 gig in size. For it, I can get rid of all but 53 gig of information, and thus will have about 247 gig free. For the other one, formatted as HFS+ and also about 300 gig in size, I can get rid of 53 gig, and that amount takes up over 97%. That partition will then have about 3 or 4 gig left.and thus about 296 gig free.

In preparation for Big Sur, I'll need to increase the sizes of the two backup partitions (looks like those will be for Carbon Copy Cloner) to about 150 gig each. Hence, mathematically that should be dooable, given how much "free space" there will be on each third partition.

I know that one way I could do this is to 1) copy all that "smaller" information from each of the "miscellaneous" partitions to flash drives (I have one that is 256 gig in size), 2) Erase and Format each SSD, and 3) create 3 new partitions (2 of them would be the backup partitions each 150 gig in size, formatted as APFS). But, doing that runs the risk of having no backups in the very short term. I would much prefer the ability to just resize the 2 backup partitions, after making the necessary room by removing what I mentioned above from each miscellaneous partition.

Would appreciate any advice, assistance, etc. for this exercise.

Last edited by MartyByrde; 02/15/21 11:55 PM.
Re: Resizing Partitions
MartyByrde #57931 02/16/21 05:20 PM
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My advice would be to back up anything you want to keep on whatever media that is handy, reformat the drive(s) APFS and put two, or more, VOLUMES on the drives and forget partitioning. Each of the volumes created on the drive is capable of occupying 100% of the drive's capacity and will expand or contract to hold whatever you put in it as needed. The read/write speeds will be slightly lower but for your intended use it shouldn't make any significant difference. I have two drives configured that way that I use for CCC backups and they are completely reliable and have worked very well.


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Re: Resizing Partitions
joemikeb #57938 02/16/21 06:46 PM
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Originally Posted by joemikeb
My advice would be to back up anything you want to keep on whatever media that is handy, reformat the drive(s) APFS and put two, or more, VOLUMES on the drives and forget partitioning. Each of the volumes created on the drive is capable of occupying 100% of the drive's capacity and will expand or contract to hold whatever you put in it as needed. The read/write speeds will be slightly lower but for your intended use it shouldn't make any significant difference. I have two drives configured that way that I use for CCC backups and they are completely reliable and have worked very well.

Thanks for the information.

So, there is no "easy" way of just resizing current partitions, even if there is plenty of free space available. Just seems so counter-intuitive.

How do I set up such volumes? Use Disk Utility for this? I am going to want to have 3 of them: 2 for each of my Carbon Copy Cloner backups, and the third for miscellaneous items.

Last edited by MartyByrde; 02/16/21 06:46 PM.
Re: Resizing Partitions
MartyByrde #57943 02/16/21 07:44 PM
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Originally Posted by MartyByrde
So, there is no "easy" way of just resizing current partitions, even if there is plenty of free space available. Just seems so counter-intuitive.
It is a function of how partitions are created and their relationship to the physical location on the drive. Whereas APFS volumes are logical structures and not tied to a specific physical location.

NOTE: You will not go too far astray if you think of a volume as "a folder that mounts, and functions, like a drive".

Originally Posted by MartyByrde
How do I set up such volumes? Use Disk Utility for this? I am going to want to have 3 of them: 2 for each of my Carbon Copy Cloner backups, and the third for miscellaneous items.
Yes you use Disk Utility. Once a drive is formatted APFS, when you select the Container in Disk Utility a +/- icon will be enabled on the tool bar. Selecting a plus will create a new partition and minus will delete a partition. Either option takes only a few seconds at most. There is an option to specify the size of a volume, but I strongly recommend ignoring it altogether and allow volumes to grow or shrink as needed. It is far more flexible.


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Re: Resizing Partitions
joemikeb #57944 02/16/21 08:04 PM
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Originally Posted by joemikeb
Yes you use Disk Utility. Once a drive is formatted APFS, when you select the Container in Disk Utility a +/- icon will be enabled on the tool bar. Selecting a plus will create a new partition and minus will delete a partition.
Nomenclature correction: Selecting "+/-" will create or delete a volume, not a partition, i.e. container.


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Re: Resizing Partitions
joemikeb #57946 02/16/21 11:18 PM
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Originally Posted by joemikeb
Originally Posted by MartyByrde
So, there is no "easy" way of just resizing current partitions, even if there is plenty of free space available. Just seems so counter-intuitive.
It is a function of how partitions are created and their relationship to the physical location on the drive. Whereas APFS volumes are logical structures and not tied to a specific physical location.

NOTE: You will not go too far astray if you think of a volume as "a folder that mounts, and functions, like a drive".

Originally Posted by MartyByrde
How do I set up such volumes? Use Disk Utility for this? I am going to want to have 3 of them: 2 for each of my Carbon Copy Cloner backups, and the third for miscellaneous items.
Yes you use Disk Utility. Once a drive is formatted APFS, when you select the Container in Disk Utility a +/- icon will be enabled on the tool bar. Selecting a plus will create a new partition and minus will delete a partition. Either option takes only a few seconds at most. There is an option to specify the size of a volume, but I strongly recommend ignoring it altogether and allow volumes to grow or shrink as needed. It is far more flexible.

OK, from what I gather, here is what I should do:

1. Launch Disk Utility.
2. Erase and Format the entire SSD as APFS.
3. Select the Container.
4. Click the "+" sign to create 3 Volumes.
5. If desired, designate a size for each volume. (If I did that, I would make each Carbon Copy Cloner backup volume 175 gig in size, and the Miscellaneous one about 150 gig).

So just to confirm, I really don't need to do #5, and the space needed for the two Carbon Copy Cloner volumes will adjust as needed.

Last edited by MartyByrde; 02/17/21 12:18 AM.

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