A "collection" of approaches to set the io scheduler for ssds on systems where both ssds and hdds are used.

10-set-ssd-ioscheduler.start

# An openrc init script (local.d) which sets the io scheduler in "/sys/block/sd?/queue/scheduler"
# for a custom list of known solid state drives.

enable=false

local_start()
{
    local ssd_scheduler
    local -a ssd_devices

    ssd_scheduler="deadline"
    ssd_devices=(
        "sda"
        "sdb"
    )

    for ssd in "${ssd_devices[@]}"; do
        if [[ -e "/dev/${ssd}" ]]; then
            echo "$ssd_scheduler" > "/sys/block/${ssd}/queue/scheduler"
        fi
    done
    
    return 0
}

if $enable; then
    local_start
fi

10-ssd-ioscheduler.rules

# An udev rule which sets the io scheduler for ssds based on "/sys/block/sd?/queue/rotational"
# in "/sys/block/sd?/queue/scheduler" automatically.
# https://wiki.debian.org/SSDOptimization#Low-Latency_IO-Scheduler

ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="deadline"