Plus Series 4-bay NAS for Offices and IT Pros Diskless 0 TB Supports RAID SHR, 0,1,5,6,10 DiskStation DS920+ Simplify the file management experience NAS with SSD cache acceleration and expandable storage capacity Synology DS920 + is an ideal network-attached storage solution that simplifies data management operations and increases productivity. Built-in dual M.2 SSD slots, support Synology SSD cache technology, can improve system I / O and application performance. The expandable capacity design, combined with Synology DX517, allows you to expand storage capacity step by step as the amount of data increases. Processor 4 core 2.0 GHz, the highest clock can reach 2.7 GHz Cache acceleration Built-in dual M.2 2280 NVMe SSD slot Efficacy 15% increase in intensive computing applications Expandability Can be expanded to 9 hard drives with a DX517 expansion unit Optimized performance and capacity DS920 + has a built-in dual M.2 SSD slot, allowing you to make good use of Synology SSD cache. Creating a cache can increase I / O response time by 20 times without occupying the front hard drive slot. With Synology DX51 model : ADATA XPG SX6000 Lite 512GB PCIe 3D NAND PCIe Internal Solid State Drive tag : NAS