Limiting SATA Link Speed to 3 Gbps on Linux Using libata.force

You can use the Linux kernel boot parameter libata.force to limit the link speed of a specific ATA port to SATA 3 Gbps (Gen2) instead of 6 Gbps (Gen3).

Example Configuration

If the target port is recognized as ata2 in Linux, add the following kernel parameter:

libata.force=2:3.0G

The format is PORT:SPEED, where PORT is the numeric portion of ata2. To configure multiple ports, separate them with commas:

libata.force=2:3.0G,5:3.0G

According to the official kernel documentation, libata.force=[ID:]VAL can be used to limit the SATA link speed on a per-port basis to either 1.5Gbps or 3.0Gbps. (Linux Kernel Documentation)

Identifying the Target Port

First, check the boot log to determine which ATA port the disk is connected to:

sudo dmesg | grep -E 'ata[0-9]+: SATA link'

Example output:

ata2: SATA link up 6.0 Gbps
ata5: SATA link up 6.0 Gbps

You can also verify the mapping to block devices with:

ls -l /dev/disk/by-path/ | grep ata

The important point is to specify the ataN number reported by Linux, not /dev/sda or the motherboard’s physical “SATA Port 2” label.

Making the Setting Persistent with GRUB

Add the parameter to the existing kernel command line in /etc/default/grub:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash libata.force=2:3.0G"

On Debian- and Ubuntu-based systems, then run:

sudo update-grub
sudo reboot

On distributions that generate the GRUB configuration differently, use either grub-mkconfig or grub2-mkconfig, depending on your environment.

Verifying the Configuration

After rebooting:

cat /proc/cmdline

Then verify the negotiated link speed:

sudo dmesg | grep 'ata2: SATA link'

Expected output:

ata2: SATA link up 3.0 Gbps

You can also check via sysfs:

cat /sys/class/ata_link/link2/sata_spd
cat /sys/class/ata_link/link2/sata_spd_limit

/sys/class/ata_link/.../sata_spd reports the current link speed, while sata_spd_limit reports the maximum speed imposed by libata. These files are read-only, so the limit is normally configured through the kernel boot parameter rather than changed at runtime with echo. (Linux Kernel Archive)

Notes

This does not throttle bandwidth; it limits the maximum SATA PHY link negotiation speed to 3 Gbps.
The ataN numbering may change if controllers are added, BIOS settings are modified, or the kernel or drivers change.
If your BIOS/UEFI provides a per-port “SATA Speed” or “Gen2” option, that may be a clearer way to configure the physical port.
This method may not apply to disks connected through USB-to-SATA adapters, NVMe, SAS, or hardware RAID controllers.