July 2025

Use eSATA Drive as SSD Cache on Synology NAS

⚠️ Disclaimer

This is an unsupported modification and may void your warranty. Proceed at your own risk.
Configuration WILL revert after DSM updates.

But why ?

Synology reserves eSATA ports for their own brand external expansion units, and DSM explicitly prevents drives connected through those ports from being used as SSD caches. The setting responsible for this behavior is called esataportcfg, found in the system configuration files.

The esataportcfg setting tells DSM which physical SATA ports should be treated as eSATA ports — usually for external expansion units like DX517.

It’s written in hexadecimal (e.g. 0x4) but actually represents a bitmask: a binary number where each bit corresponds to a SATA port on the motherboard.

0x4 is hexadecimal for binary 0100. This means:

• Port 0: 0 = Not eSATA
• Port 1: 0 = Not eSATA
• Port 2: 1 = eSATA
• Port 3: 0 = Not eSATA

DSM will treat only port 2 ( sdc ) as eSATA, and ignore it for caching, system volumes, and other features limited to “internal” drives.

This is useful if you want to explicitly allow or deny eSATA functionality for certain ports — for example, if you’re using a third-party eSATA dock or expansion device and want DSM to handle it differently. ( I have NOT tried that yet !)

The “hack”

1. Enable SSH in DSM:
   Control Panel → Terminal & SNMP → Enable SSH service
2. SSH into your NAS: ssh romain@synology
3. Edit the config files: sudo vi /etc.defaults/synoinfo.conf If it exists, also edit: sudo vi /etc/synoinfo.conf
4. Find the line: esataportcfg="0x4" And change it to: esataportcfg="0x0"
5. Unmount ISCSI & Reboot your NAS: sudo reboot

After Reboot: Enable SSD Cache

Once DSM is back online:

• Go to Storage Manager → SSD Cache
• Select your connected SSD (formerly on the eSATA port)
• Create a read or read-write cache as desired

DSM should now accept the drive as a valid caching candidate.

Notes

• This trick works best on models with physically exposed eSATA ports not already assigned to expansion bays.
• DSM updates may overwrite synoinfo.conf. Consider making a backup.
• This workaround does not make sense if you have M.2 slots — use those instead for best performance.

Let me know if it helped !