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An easy way to do this is format the T5 Drive to APFS if you are using Mojave or later and then use CCC Carbon Copy Cloner or SuperDuper software to clone the iMac to the T5 external drive

Another option is to Format the T5 drive to APFS and 1) install macOS ( Mojave? / Monterey?) and 2) then use migration assistant to transfer the data and system preferences
 
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Another option would be to use Apple's built-in disk utility to create a direct copy of your existing internal drive onto the external one. If I'm not mistaken it should still be able to create a bootable copy of your macOS installation, although you might have to boot into Recovery Mode to make ensure filesystem consistency.
 
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^^This.

If I recall correctly, was able to clone a Catalina drive to external SSD using Disk Utility in recovery mode. Restore option.
 
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It would help if you told us WHICH iMac you have,
WHAT YEAR it was made,
What OS is on it.

Easiest, fastest way:
Just download a copy of SuperDuper (free to use for this purpose).
Then clone over the contents of the internal to the t5.

The t5 MUST be formatted correctly before you try this.
I would REMOVE all the Samsung software -- you don't need it.
For High Sierra and earlier, format to "Mac OS extended with journaling enabled, GUID partition format".
For Mojave and later, format to "APFS, GUID partition format".
 
I clicked on "Erase" and it shows Format and Scheme.
I selected APFS for Format.
Would the Scheme be GUID Partition Map? (Other options are "Master boot record" and "Apple partition map")
 
OP:

Tell us WHICH VERSION of the OS you're using, so we can tell you which format to use.

They ARE NOT all the same!
 
I let it run, and when I checked it, says: "failed to copy files.."
It says 1005 GB evaluated, 991 GB is copied.
Maybe could it be that there wasn't enough space for T5 compared to my hard drive?

(When I started to copy files, it did say that there was a little more than 1.03tb on my iMac hard drive, but I have 24 gb gb left in my iMac drive.)
 
t did say that there was a little more than 1.03tb on my iMac hard drive, but I have 24 gb gb left in my iMac drive.)

How large is the T5? I hope it is at least 2 TB. You need a minimum of 200-300 GB free on a 1 TB drive.
 
My T5 is 1TB.

I could buy a new 2TB one but then I wouldn't know what to do with my 1TB one.
 
I could buy a new 2TB one but then I wouldn't know what to do with my 1TB one.

You could use it as one of your 3-2-1 backups. Not ideal with just 24GB free, but since the drive would be wiped, repopulated, and used only for backup purposes it should work.

Otherwise you need to find a way to delete at least 200 GB from the drive.
 
I am trying to buy a 2TB one to make it easier.
I see that on Amazon, T5 is about $280 and T7 is about $200.

I'm leaning towards T7 because of the price, but I think I've read some reviews about it having overheating issues.

Looking at the reviews, it looks like some people had connection issues and data loss. Anyone have experience?
 
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OP asks:
"What could happen if I have less than 200 GB free?"

Nothing.
IGNORE what was posted above about "needing 200gb free"
Absolute nonsense.

Personal example:
I have a 2021 MacBook Pro 14" running Monterey.
It has about 106gb used or so (total disk size is 512gb).
I created a cloned backup on a 128gb SSD I had laying around.
The backup boots and runs fine, even though there is little free space left (about 10+/-gb).
It works.
 
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I'm copying my Mac again into T5 (after clearing some files first from Mac). Before copying it said something like "this will copy all files except temporary or specific application files" What could those files be?
 
I finished moving the files, and now I want to boot from it.

As I restarted the iMac, I pressed the option button, but it went straight into my iMac as normal without giving an option to boot from T5. What am I missing?
 
What could happen if I have less than 200 GB free?

The 20-30% rule was originally for hard disks. Once you reached that number the number of seeks to find open blocks on a highly fragmented drive would start to slow the system and could cause a system crash if the disk started thrashing.

With SSD's it is more complicated with effectively no seek time time and over provisioning to keep cells from wearing out. The greater the over provisioning and free space the better the performance and lifespan of the SSD, within limits. Not totally sure how to balance the provisioning and free space numbers on an SSD so I just fall back on the old rule just to be safe. Assume you could reduce the free space requirement if you have a high provisioning number.

As the cart below shows you can get 60% better performance with 20% vs 0% provisioning. The colored lines are for different SSDs.

Screen Shot 2022-12-18 at 02.22.43.png

 
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OP wrote:
"I finished moving the files, and now I want to boot from it."

Fishrrman dumb question:
HOW did you "move" the files?

Did you use either SuperDuper or CarbonCopyCloner?

Try this:
a. Open system preferences
b. Click "startup disk"
c. Does the t5 "show up" there as a bootable option?
 
The 20-30% rule was originally for hard disks. Once you reached that number the number of seeks to find open blocks on a highly fragmented drive would start to slow the system and could cause a system crash if the disk started thrashing.

With SSD's it is more complicated with effectively no seek time time and over provisioning to keep cells from wearing out. The greater the over provisioning and free space the better the performance and lifespan of the SSD, within limits. Not totally sure how to balance the provisioning and free space numbers on an SSD so I just fall back on the old rule just to be safe. Assume you could reduce the free space requirement if you have a high provisioning number.

As the cart below shows you can get 60% better performance with 20% vs 0% provisioning. The colored lines are for different SSDs.

View attachment 2129895

Is the blue NVMe?
 
Another option would be to use Apple's built-in disk utility to create a direct copy of your existing internal drive onto the external one. If I'm not mistaken it should still be able to create a bootable copy of your macOS installation, although you might have to boot into Recovery Mode to make ensure filesystem consistency.

I wasn't aware of this option. I'll have to check it out next time I run it.
 
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