ramdisk create/delete on Mac OS X.

ramdisk.sh

#!/bin/bash

# From http://tech.serbinn.net/2010/shell-script-to-create-ramdisk-on-mac-os-x/
#

ARGS=2
E_BADARGS=99

if [ $# -ne $ARGS ] # correct number of arguments to the script;
then
  echo " "
  echo "To create a RAMDISK -> Usage: `basename $0` create SIZE_IN_MB"
  echo "To delete a RAMDISK -> Usage: `basename $0` delete DISK_ID"
  echo " "
  echo "Currently this script only supports one RAMDISK. Will update soon."
  echo "DISK_ID can be shown with 'mount'. usually /dev/disk* where * is a number"
  echo " "
  echo " "
  exit $E_BADARGS
fi

if [ "$1" = "create" ]
then
  echo "Create ramdisk..."
  RAMDISK_SIZE_MB=$2
  RAMDISK_SECTORS=$((2048 * $RAMDISK_SIZE_MB))
  DISK_ID=$(hdiutil attach -nomount ram://$RAMDISK_SECTORS)
  echo "Disk ID is :" $DISK_ID
  diskutil erasevolume HFS+ "ramdisk" ${DISK_ID}
fi

if [ "$1" = "delete" ]
then
  echo "Delete/unmount ramdisk $2"
  umount -f $2
  hdiutil detach $2
fi

Since tmpfs dropped on macOS 15 (Sequoia), you can also use it to create RAM disks, and this approach has two massive advantages over the hdiutil/diskutil-based implementations:

• Incomparable performance: around GB MB/s read/write on my M1 Max Mac Studio (makes sense since it's basically a native filesystem directly managed by the VM)
• Dynamic RAM allocation: RAM isn't "reserved" ahead of time, but usage grows with the amount of data you put on the RAM disk (10 MB of data on a 10 GB RAM disk = 10 MB of RAM used)

You can easily mount a tmpfs volume with the following commands:

• sudo mount_tmpfs -s 10G path/to/dir — mounts the volume and temporarily hides the original folder contents
• sudo chown $(whoami):staff path/to/dir — to get write permissions back inside the volume

Same goes for unmounting:

• sudo umount path/to/dir — heads up, all volume contents vanish instantly, original folder files reappear

To bypass these mount/unmount "hiccups", I built a utility called RAM Folder that turns any of your folders into a tmpfs volume by importing the data into it when mounting, and saves the volume's contents back to the folder when unmounting.

Turns out the transition between a standard folder and a RAM disk is so seamless that I decided to call it: RAM Folder.

It's not open-source (yet) but you can check it out on the RAM Folder product page and there's a 14-day trial free trial.
It's super performant for build caches, hosting a unit test DB, or honestly any operation that's IO-bound.

Hope you find this interesting and take the time to give the utility a spin!