DS3018xs supports up to 30 drives with two Synology DX12152 expansion units, allowing you to start small and easily scale up on demand. In addition to 10GbE add-on cards, which can upgrade the network capacity of DS3018xs, the PCIe slot also supports the optional PCIe M.2 SSD adapter card M2D173 for dual M.2 SSD slots to function as SSD cache for greatly enhanced storage performance without using the 3.5" drive bays.
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