Synology DS918+ versus DS1517+ NAS

DS918+ 4-Bay NAS vs DS1517+ 5-Bay NAS – Which Synology should you Buy?

Synology DS918+ and DS1517+ are both equally powerful NAS models. DS918+ is made with multimedia capabilities whereas DS1517+ comes with a focus on basic NAS functions.  Gen2 x8 slot (x4 link) lets you add 10GbE or cache card to massively increase IOPS of a device.

Both processors have very similar benchmark scores even though one is Intel Atom and other Intel Celeron. They both come with built in encryption engine, but only DS918+ has transcoding engine built in.




DS918+ has 4 drive bays but DS1517+ has 5, what is better?

Having this extra 1 bay makes quite a difference if you are very concerned about service reliability. With 5 drives, you can set up RAID6 protection and still have decent storage capacity available. With RAID6 on 4 drives, your available storage capacity would be the total of 2 drives not three. If you need this 2 drive failure protection choose a 5 bay not four bay. Normally people choose one drive redundancy option (RAID 5).

Which one can be expanded?

Both NAS models can be expanded. Number 9 in model number DS918+ means – it can be be expanded up to 9 drives with a expansion box. DS1517+ can be expanded up to 15 drives with expansion units attached.

Can I set up cache on DS1517+ and DS918+

DS1517+ comes with PCI port which can be used for M2D17 card for M.2 SSD. With that installed, you can have cache enabled reaching 500MB/s internal speeds.

DS918+ comes with 2 M.2 SSD slots at the bottom of a NAS. These are NVMe slots- reaching 2000MB/s speed and more. So answer is yes, you can have cache on both of the boxes. But DS918+ will have much faster cache.

What is the difference in network ports?

DS1517+ comes with four 1Gbe network ports. With a link aggregation enabled- you could potentially reach 400MB/s transfer speeds. It get even better. You can install 10GbE card in a available PCIe slot. With a correct RAID setup and fast SSD drives you could potentially reach 1GB/s. That is HD movie a second. Perfect solution for Video editors.

DS918+ has only 2 ports (1GbE) which will let you do transfers of a maximums around 200MB/s. Nowadays all 2 and more bay NAS should come with 10GbE support, but it still doesn’t happen.

Which one fit at home better?

DS1517+ (26.2 dB(A))  fan operates in two modes:

  • Cool Mode
  • Quiet Mode

DS918+ (19.8 dB(A)) fan works in:

  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode

If noise is an issue, DS918+ will do a better job in home environment. Also power consumption is different. DS1517+ operates at 42.1 W (Access) and 23.1 W (HDD Hibernation). DS918+ operates at 28.8 W (Access) and 12.6 W (HDD Hibernation).

Transcoding performance difference between DS1517+ and DS918+

The most important difference between these two NAS models is transcoding engine. DS918+ unlike DS1517+ has one. Video playback app such as DS Video will be able to access this transcoding engine on the CPU to do video conversion without effecting overall performance of the processor. If NAS is used for multiple things, other services will not suffer from performance shortage during video transcoding process.

As this table shows, DS1517+ can cope with Full HD video transcoding, but DS918+ can go step further and transcode some most popular 4K video formats.


Maximum Transcoding Channel Number
  • 1 channel, 30 FPS @ 1080p(1920×1080), H.264 (AVC)/MPEG-4 Part 2 (XVID, DIVX5)/MPEG-2/VC-1
  • 2 channel, 30 FPS @ 4K (4096 x 2160), H.264 (AVC)/H.265 (HEVC) or
    2 channel, 30 FPS @ 1080p (1920×1080), H.264 (AVC)/H.265 (HEVC)/MPEG-2/VC-1

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