User profile for user: Angie3M
Angie3M Author
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Using external SSD for Time Machine AND scratch disk space?

I have a new Samsung SSD T7 1TB and successfully set it up & ran Time Machine. I also wanted to use it for scratch disk space, but it doesn't show up as an option in Photoshop. Adobe told me I couldn't do both and sent me to Samsung, Samsung said I could do both and the SSD seems to be working, so they sent me to Apple, so here I am. Do I need to create a partition? Anyone have any thoughts?


I am NOT a techie. I'm doing simple tasks in Photoshop, but don't have much room on my laptop, so running into errors. My Time Machine back up is 163MB. I'm on a MacBook Air, M1, 2020 running Sonoma 14.6.1.

MacBook Air 13″, macOS 14.6

Posted on Mar 3, 2025 7:52 AM

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User profile for user: Tesserax
Tesserax
User level: Level 10
158,562 points

Posted on Mar 3, 2025 9:56 AM

Ok, let's start with why you shouldn't use the same drive for both Time Machine (TM) backups and for basic file storage.


As it relates to TM:

  • The ideal storage capacity of the TM backup drive should be 2-3x the size of the internal drive (the one in your MacBook Air). So, if your Mac's internal drive is only 256GBs, then your 1TB SSD would be adequate for TM only. If that internal drive is larger, say 512GB or 1TB, then you would need a larger SSD.
  • TM wants to use the entire drive's volume. It doesn't "like" to share that volume with anything else. That would mean that you would want to partition (split) the drive into, at least, two partitions: one for TM, and the other, for file storage. You can quickly see that this 1TB drive will not have enough storage space for both.
  • If your data is critical to you, it is never a good idea to use a single backup strategy ... as drives can fail. As such, please use the following as a suggest reference: macOS Backup Strategy


What are your options? Basically, you have two:

  1. Use this SSD for storage or TM only. Then get a second drive for the other purpose. Note that for either purpose, an SSD is NOT required. You will find that HDDs can be had at a much lower price point per GB than SSDs. Neither of these purposes will actually benefit by using an SSD.
  2. Go ahead and partition the drive into two partitions to use for both. (Not recommended)
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User profile for user: Tesserax
Tesserax
User level: Level 10
158,562 points

Mar 3, 2025 9:56 AM in response to Angie3M

Ok, let's start with why you shouldn't use the same drive for both Time Machine (TM) backups and for basic file storage.


As it relates to TM:

  • The ideal storage capacity of the TM backup drive should be 2-3x the size of the internal drive (the one in your MacBook Air). So, if your Mac's internal drive is only 256GBs, then your 1TB SSD would be adequate for TM only. If that internal drive is larger, say 512GB or 1TB, then you would need a larger SSD.
  • TM wants to use the entire drive's volume. It doesn't "like" to share that volume with anything else. That would mean that you would want to partition (split) the drive into, at least, two partitions: one for TM, and the other, for file storage. You can quickly see that this 1TB drive will not have enough storage space for both.
  • If your data is critical to you, it is never a good idea to use a single backup strategy ... as drives can fail. As such, please use the following as a suggest reference: macOS Backup Strategy


What are your options? Basically, you have two:

  1. Use this SSD for storage or TM only. Then get a second drive for the other purpose. Note that for either purpose, an SSD is NOT required. You will find that HDDs can be had at a much lower price point per GB than SSDs. Neither of these purposes will actually benefit by using an SSD.
  2. Go ahead and partition the drive into two partitions to use for both. (Not recommended)
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Using external SSD for Time Machine AND scratch disk space?

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