The DS15xx+ and DS18xx+ have always been my go to solutions when I needed a workhorse NAS. I currently run a DS1815+ as my primary NAS and an older DS1511+ has been a reliable backup destination since it was replaced by the DS1815+. Synology updated both those models for 2017, releasing a DS1817+ and a DS1517+.
The press release calls them “5-bay and 8-bay tower servers” which, while not completely incorrect, could be misleading. They are oriented horizontally and appropriate for a shelf. They don’t take a lot of space vertically.
They support the new M2D17 M.2 SATA SSD adapter or a 10GbE network interface card, both of which are optional. The M2D17 allows setting up SSD caches without using an internal bay.
Each NAS also support up to two of the new DX517 expansion units. Each DX517 adds 5 drive bays. The new models can be expanded to 16GB of memory which is now faster dual channel memory.
The two new models, along with the new expansion unit, all come with a 3 year warranty. This can be expanded to 5 years in some countries.
While they aren’t available for delivery at this time, only pre-order, Amazon (US) lists the DS1817+ w/8GB RAM for $950 and the DS1517+ w/2GB RAM for $700. These are about the same as the prices for the previous models when they were originally released, although the price has dropped now that they are the old models. This is especially true for the DS1815+ which is down to $835 (w/2GB RAM) on Amazon and B&H Photo.