Due to the specification limits of the SATA controllers used in Synology DS415+, DS1515+, and DS1815+, the maximum transmission speed varies depending on the drive bay.

If you have already created a storage volume in DS415+, DS1515+, or DS1815+ but the SSDs used as system cache are not installed in Drive Bay 1 or Drive Bay 2, please refer to the following steps to change the configuration:

1. Do not modify any system settings.
2. Shut down your Synology NAS device.
3. Remove all drives from the drive bays.
4. Install the SSDs into Bay 1 and Bay 2, and the rest of the HDDs into the other drive bays.
5. Power on the Synology NAS device.
6. Go to DSM > Storage Manager and confirm the status of the storage volume and SSD cache settings.

If you need to enable SSD cache on one of these models, please install the SSDs into Drive Bay 1 or Drive Bay 2, each with a transmission speed of SATA 6.0 Gb/s to achieve optimal performance. There are no SSD installation limitations for other Synology NAS models.