Cross-platform way of determining if on SSD?

Question

I'm writing a tool in Rust which needs to vary its functionality depending on whether the current filesystem is an SSD or a traditional hard drive.

The difference at runtime will be that if the files exist on an SSD, more threads will be used to access files versus an HDD, which will only thrash the disk and reduce performance.

I'm primarily interested in Linux, as that is my use case, but welcome any other additions. I also need to do this as a non-root user if possible. Is there a syscall or a filesystem device which will tell me what kind of device I'm on?

Answer 1

Credit goes to @Hackerman:

$ cat /sys/block/sda/queue/rotational
0

If it returns 1, the given filesystem is on rotational media.

I have fleshed this concept out into a shell script which reliably determines whether a file is on rotational media or not:

#!/bin/bash

set -e

# emits the device path to the filesystem where the first argument lives
fs_mount="$(df -h $1 | tail -n 1 | awk '{print $1;}')"

# if it's a symlink, resolve it
if [ -L "$fs_mount" ]; then
  fs_mount="$(readlink -f $fs_mount)"
fi

# if it's a device-mapper like LVM or dm-crypt, then we need to be special
if echo $fs_mount | grep -oP '/dev/dm-\d+' >/dev/null ; then
  # get the first device slave
  first_slave_dev="$(find /sys/block/$(basename $fs_mount)/slaves -mindepth 1 -maxdepth 1 -exec readlink -f {} \; | head -1)"
  # actual device
  dev="$(cd $first_slave_dev/../ && basename $(pwd))"
else
  dev="$(basename $fs_mount | grep -ioP '[a-z]+(?=\d+\b)')"
fi

# now that we have the actual device, we simply ask whether it's rotational or not
if [[ $(cat /sys/block/$dev/queue/rotational) -eq 0 ]]; then
  echo "The filesystem hosting $1 is not on an rotational media."
else
  echo "The filesystem hosting $1 is on rotational media."
fi

The above works for me both on plain partitions (ie /dev/sda1 is mounted at a given path) and on dm-crypt partitions (ie /dev/mapper/crypt is mounted at a given path). I have not tested it with LVM because I don't have one nearby.

Apologies for the Bash not being portable.