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User profile for user: dba_Fred
dba_Fred Author
User level: Level 1
4 points

Different OSs and Sizes

I have various USB iMacs and Mac laptops and I want to partition a hard drive with different versions of OSs for external booting. I want to know how large a partition to create for each different OS.

I’m hoping this is a list on this site or could be pointed to a website with this information.


I have a blank SSD external drive or could obtain a SATA drive or thumb drives for this.


I’m new posting to but not reading this community and have used Apple computers from a IIe to my new Mid-2017 iMac.


Thank you for your assistance.

iMac 21.5" 4K, macOS 10.13

Posted on Jun 20, 2019 2:32 PM

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User profile for user: DonH49
DonH49
User level: Level 6
16,710 points

Posted on Jun 20, 2019 2:36 PM

I do that function frequently. If you are going to install a system then boot from it and update that system then 30 to 35 gigs each partition. You could get away with 25 but sooner or later you'll need the slightly larger. This is using a 240 gig SSD partitioned.


If you are going to use Apple's create media method for INSTALLING system then 12 gigs is minimum. This method is for booting the installer and installing onto a drive.



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User profile for user: DonH49
DonH49
User level: Level 6
16,710 points

Jun 20, 2019 2:36 PM in response to dba_Fred

I do that function frequently. If you are going to install a system then boot from it and update that system then 30 to 35 gigs each partition. You could get away with 25 but sooner or later you'll need the slightly larger. This is using a 240 gig SSD partitioned.


If you are going to use Apple's create media method for INSTALLING system then 12 gigs is minimum. This method is for booting the installer and installing onto a drive.



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User profile for user: BDAqua
BDAqua
User level: Level 10
245,183 points

Jun 20, 2019 2:42 PM in response to dba_Fred

It depends if you wan't to do anything within the OSes, which would require much more space.


diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *500.1 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS Macintosh HD 499.2 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3


/dev/disk1 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *6.0 TB disk1

1: Apple_HFS 10.8 750.1 GB disk1s1

2: Apple_HFS 10.13 601.2 GB disk1s2

3: Apple_Boot 650.0 MB disk1s3

4: Apple_HFS 1012 748.3 GB disk1s4

5: Apple_Boot 650.0 MB disk1s5

6: Apple_HFS 10.10 749.6 GB disk1s6

7: Apple_HFS 10.9 749.6 GB disk1s7

8: Apple_Boot Recovery HD 650.0 MB disk1s8

9: Apple_HFS 10.11 750.1 GB disk1s9

10: Apple_HFS 10.7 750.1 GB disk1s10

11: Apple_HFS 10.6 275.1 GB disk1s11

12: Apple_HFS 274.9 GB disk1s12

13: Apple_HFS 199.9 GB disk1s13

14: EFI EFI 209.7 MB disk1s14


/dev/disk2 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *2.0 TB disk2

1: EFI EFI 209.7 MB disk2s1

2: Apple_HFS Mercury Elite 1TB 1.0 TB disk2s2

3: Apple_HFS 10136 999.4 GB disk2s3

4: Apple_Boot Recovery HD 650.0 MB disk2s4


/dev/disk3 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *127.9 GB disk3

1: Windows_FAT_32 NO NAME 127.9 GB disk3s1

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User profile for user: dba_Fred
dba_Fred Author
User level: Level 1
4 points

Jun 21, 2019 3:08 AM in response to dba_Fred



Thank you Smokerz and BDAqua, those replies are helpful and useful. 


The partition sizes listed in BDAqua’s post prompt a follow up question/request for clarification.

I install the OSs in say 50 GB partitions on the external drive. I boot the computer from the appropriate volume on the external drive and when it’s done, I’m looking at the Finder. At that point I run the application(s), say Safari or Pages, located on the computer’s internal drive. Any changes or saves I make would be saved to the internal drive, not the external boot volume. 

But if I booted from the OS on the external drive and launched  applications located on the external drive, then any changes would be made to the OS on the external drive (saving to the internal drive any changes I made to new or existing files).


Is that thought process correct?

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User profile for user: dba_Fred
dba_Fred Author
User level: Level 1
4 points

Jun 21, 2019 6:18 PM in response to BDAqua

Ahh, the fog is clearing (even tho I live in the Desert Southwest, I still often find myself in a fog 😉


Based on the sizes you have to run the computer from an external hard drive, BDAqua, it looks like I’ll want to set up the external drive as Smokerz described, with both a boot partition and an installer partition for each OS. That way I can boot the computer from the external drive to test or repair the computer and then if necessary, do a fresh install of the OS to the computer’s internal drive.


I owe Smokerz and BDAqua a beer.


Happy Macing (or is it Maccing?) 😃

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Different OSs and Sizes

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