Ramdisk on macOS Mojave/Catalina?

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un.homme Author

Level 1

13 points

Ramdisk on macOS Mojave/Catalina?

What is the modern way the create a ramdisk on macOS Mojave or Catalina?

Specifically, how to:

- create a ramdisk for one-time use, discarded when shutting down the Mac?

- dismount & destroy the ramdisk, freeing up memory?

- create an empty ramdisk automatically when booting the Mac?

- create a ramdisk with a few specific folders created, when booting the Mac?

- Persist the content of a ramdisk when shutting down a Mac, and reload that content into a ramdisk when the Mac starts again?

Also… On Mojave/Catalina, would the newer APFS file system be more appropriate for a ramdisk than HFS+ file system?

Example of old solutions for a 1-gig drive (1 gig = 1024 * 2048 = 2097152) named `RamDisk`:

diskutil erasevolume HFS+ 'RamDisk' `hdiutil attach -nomount ram://2097152`

I have also found this snippet that seems to be using the APFS file system. But I don't understand the parts, and don't know if this is a proper way or not.

diskutil partitionDisk $(hdiutil attach -nomount ram://2097152) 1 GPTFormat APFS 'RamDisk' '100%'

Posted on Oct 3, 2019 12:31 PM

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Answer 1

Best reply

un.homme Author

Level 1

13 points

Oct 7, 2019 5:25 PM in response to Kurt Lang

Not helpful. Does not address the Question.

And incorrect.

A RamDisk will be far faster than SSD storage.

And SSD storage wears out on writes. RAM does not.

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Answer 2

Oct 14, 2019 9:57 AM in response to un.homme

The method you mention last seem to work.

Create and mount to /Volumes/ramdisk

NUMSECTORS=1000000                                                  # a sector is 512 bytes
MYRAMDISKDEVICE=`hdiutil attach -nomount ram://$NUMSECTORS`.        # eg /dev/disk4
diskutil partitionDisk $MYRAMDISKDEVICE 1 GPTFormat APFS 'ramdisk' '100%'

Unmount and free memory

diskutil eject /Volumes/ramdisk
diskutil eject $MYRAMDISKDEVICE                                     # eg /dev/disk4

Reference

https://stackoverflow.com/questions/46224103/create-apfs-ram-disk-on-macos-high-sierra

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Answer 3

Oct 7, 2019 5:35 PM in response to un.homme

If you are going to quote the pros maybe it is worthwhile stating some cons:

Requires a battery when system is powered off
If battery fails & power fails, data is lost
High cost per gigabyte of memory

But regardless, hopefully someone will stop by to specifically answer your question.

In the meantime, this article may help: https://blog.macsales.com/46348-how-to-create-and-use-a-ram-disk-with-your-mac-warnings-included/

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Answer 4

Kurt Lang

Level 9

58,284 points

Oct 3, 2019 1:00 PM in response to un.homme

If you have an SSD in your Mac, a RAM disk is pointless.

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Ramdisk on macOS Mojave/Catalina?

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