Synology DS918+ NAS or a PC?

Submitted by peter on Tue, 11/07/2017 - 00:12

The Synology DS918+ NAS, Network Attached Storage, device can hold 4 disks in any combination of arrays to give you easy access to a mass of data. How does the $799 purchase price compare to a regular PC built for the same work?


NAS is Network Attached Storage. A NAS device holds from one to many disks. A one disk NAS has no redundancy which means you lose the data when the disk breaks. A two disk NAS can use RAID 1 for redundancy but you lose 50% of the space. A four disk NAS can use RAID 5 for redundancy with only a 25% loss due to redundancy.

Most NAS devices have an Ethernet connection to your router so you can share the data across your wired and wireless network. You can get NAS with built in wireless but the wireless is soon out of date. Use a wireless router or a separate USB wireless adaptor or build your own PC based NAS with a replaceable wireless card.


There are no disks in the DS918+. You have to supply your own disks. You could recycle your existing disks. I have a few one and two terabyte disk I could use in a NAS device. You need up to four disks. For a RAID array, you need disks the same size.

The cheapest local 3.5" magnetic disk is $64 for 1 TB. You could put four of them in a RAID 5 array to produce 3 TB of redundant storage for $256.

You could use 12 TB disks at $940 each ($104 per TB in RAID 5) or 10 TB disks at $590 each ($78 per TB) or 8 TB disks at $360 each ($60 per TB).


The Synology device uses an Intel Celeron J3455 which has a benchmark of 2170. You can buy an Intel Celeron G3930, with a benchmark of 3053, for just $49. From my experience of Synology devices and equivalents from Qnap, the processors are just fast enough to perform basic NAS functions and run out of power when you start using the other features of the device. Buying a faster processor will give you the margin to run other services.


The DS918+ has two DDR3 memory slots with 4 GB of memory in one slot. You can add another memory card to get 8 GB for running multiple services.

A plain microATX PC motherboard has two slots for the slightly faster DDR4 memory. You can insert 2 cards of 4 GB each for $129. You get the extra memory to run additional services. You also get lots of memory to cache directories from large disks. When you are using disks above 2 TB, you will benefit from more than 4 GB of memory.


You need a motherboard to hold the processor and the memory. Your own build can use a really cheap motherboard. For $120, you can get an excellent motherboard with outputs for HDMI, DVI, and VGA. This lets you run a television straight off your NAS for monitoring activity or watching the news while you run a backup or for editing video.

For editing video, you might spend a little extra for a faster processor or a graphics card. When you build your own, you can choose exactly what you need and upgrade at a later date.


The DS918+ has a neat little case for four disks. You can buy a neat midi size case for $100 with space for more than four disks. You could add a few extra dollars to the motherboard price to get six SATA sockets instead of four SATA sockets then expand to size disk drives. There are so many options for cases, hundreds, that you can plan for many years into the future.

M.2 drive

The DS918+ has slots for two M.2 drives in the 2280 size. Motherboards usually have only one M.2 drive and they often allow an M.2 drive larger than 2280. You will not see a performance difference between a couple of M.2 drives in the Synology device and a single good M.2 drive in a good motherboard.

Network connections

The DS918+ has two Gigabit Ethernet connections. Motherboards give you one or two Gb connections. Some have built in Wifi. There is a huge range of connection options. The motherboards also have many USB connections to accept the latest network adaptors. Your own build will give you flexibility for many years.


The DS918+ provides the comprehensive software from Synology and you are limited to whatever Synology provide. There is a possibility that you will run into problems when you start using functions outside the pure NAS functions.

Your own build will use a distribution of Linux. You might add preconfigured software like <a href="/openmediavault">Openmediavault</a>. You can add anything you like. You can use the latest version of everything. You can have multiple versions of every type of software and compare them against each other.

I tried to use Qnap software in a NAS configuration then add just one more service. The result was horrible. Synology are better at some things, compared to Qnap. I still prefer to use a standard distribution of Linux and use the latest versions of all the standard software configured the way I want it configured.


RAID is supposed to make disk storage more reliable. You run into many problems when a disk fails and you start to rebuild a RAID array. For a start, you need lots of spare processing power to build the array in the background while the NAS is running. The replacement disk has to be at least as large as the dead disk. Some RAID configurations create a heap of other problems.

Synology only support their version of RAID. What happens when the DS918+ breaks and you have to recover the RAID array in a different machine? You either buy a matching Synology device or you give up. A linux RAID array can be configured for recovery in a completely different machine.


The DS918+ has an external eSATA port to fit an extension box with another four drives. Given the temporary nature of an external cable connection, you would configure a separate array in each box. Using RAID 5, you would use eight disks and have the storage of six disks.

Your own build could use a full tower case for up to eleven disks. With RAID 5, you could have one array with storage equivalent to ten of the disks.

Your own build will have one M.2 device, four or six SATA connectors, and can have several PCI expansion slots. You can add an extra M.2 slot through an expansion card for just $22. Four port SATA expansion cards start at $40.

Adding expansion cards can be messy. I would stick to what you get on a motherboard, six SATA connectors, and buy larger capacity disks.


The DS918+ is $799 before disks and $814 delivered. Your own build, using the hardware mentioned here, is just $398 before disks and delivery. You then add in your own time. Using something like Openmediavault will chew up a similar time to your first use of a Synology style device.


The Synology DS418 is another option at just $598. The DS418 has half the memory, compared to a DS918+, a slower processor, and a hardware chip for video transcoding. Tests suggest it is just as good for delivering one stream of transcoded video. With only 2 GB of memory, the DS418 is unlikely to work with any other services switched on.

Western Digital have a 4 drive NAS for $530 but it has only a Marvell processor. I would not bother with the WD produce for anything other than a slow backup.

A Qnap TS-431P costs only $360, has little memory and not much processing power. My experience with Qnap devices is not good. I threw one out as a noisy slow device. Find someone who owns a current model Qnap before purchase.

The Qnap TS-453A looks more interesting and is a similar price to the Synology DS918+. The TS-453A has four Ethernet connections. You might be able to backup several computers without placing the network traffic on your regular network. The TS-453A also has two HDMI sockets, giving you the option to display the device activity on one screen and a video stream on the other. You could use it similar to a build your own PC based NAS. The main limit will be the low power processor.

Power usage

The Synology device uses less power than a PC based NAS and has limited expansion. Your own build will start with more power usage and will let you expand past a DS918+, giving you a cost/power saving for larger configurations.

In your own build, you are free to choose things like disk usage, giving you some choice between response time and power savings.


Small cases always make more noise than larger cases with smoother air flow. Large cases accept large fan. Your own build can start with the fans provided with the processor and the case then graduate to better fans to reduce noise.

The medium size case next to me has Noctua fans. I have to look at the indicator light to check if the machine is on. Your own build saves $400. If noise is an issue, you could spend $100 on Noctua fans and still be $300 ahead.


The Synology device is close to green given that it uses the minimum hardware and electricity to provide a four drive NAS. Your own build uses more resources to build a NAS and more electricity to run the NAS. Your build is greener when you can recycle parts, an exiting PC, disks, anything significant.

Your own build also qualifies for a green approach when your build includes things that would have to be added on to a prebuilt NAS. Take the example of attaching a screen to display an incoming data stream. You have HDMI and other video outputs on your own build. The Synology device requires a connected PC just to run the screen.


The Synology style device is a quick easy way to set up storage. A company will save expensive people time using that type of device. A company is unlikely to use the extra functionality provided by the software. Instead a company would buy a dedicated device/server for each function.

For your own use, the flexibility of a small PC build will open up many options in the future. You have the option to recycle any combination of disks. When you change networks, you unplug the old adaptor and plug in the new adaptor. This is what I choose for long term flexibility.