Test: WD Red SN700 – behöver du en NAS-SSD?

Western Digital reuses components from the SN750 and releases a new SSD for NAS. WD Red SN700 wants to accelerate your big data storage.

Western Digital’s Red Series of hard drives have long been popular (as long as they don’t use SMR) as storage media in NAS boxes for home users and small businesses. They have some technology that was previously exclusive to more expensive disks designed for data centers and servers. This makes them more expensive than standard consumer drives, but also more stable and better suited for RAID, which is often used in NAS devices.

To improve performance, the major NAS manufacturers have started to build support for different types of cached storage or tiered storage into their NAS boxes. Then an SSD is used to cache frequently used data or to provide access to a faster level of storage, to increase performance. For those who only use their NAS as file storage, it doesn’t matter that much, but for those who use their NAS as a server (which most people do), using a faster SSD for better performance can make a huge difference.

Of course, WD doesn’t just want to sell you the disks you will have in your NAS, they also of course want you to buy a cache SSD from them. Their previous drive was SATA based and both took up unnecessary space in your NAS and wasn’t very fast either. Now they are launching a new SSD in the Red series with the name WD Red SN700.

Specifications

If we look at the specifications, the WD Red SN700 is very similar to the WD Black SN750, on which it is based. WD hasn’t confirmed which memory chips the new device uses, but our guess is that it’s BICS4 (the SN750 uses BICS3), which would make the SN700 more similar to the SN730 – an OEM version of the SN750, but with BICS4 NAND. Of course, what stands out a bit is the device’s warranty. Like so many others, the drive has a five-year warranty but it also has a TBW value of a whopping 2000TB, which is significantly more than Black’s 600. For the 1TB model, that results in DWPD (Drive Writes Per Day) of just over 1 DWPD, which is not bad at all for a consumer device. Otherwise, the specifications appear to be very similar between the models.

Models

It’s been a long time since we tested a device that comes in so many versions. The SN700 is available from 250GB all the way up to 4TB. There aren’t many other devices on the market that can match it.

If we look at the performance figures and the BTW value of the different models, we see that the value rises as we are used to from 250 GB up to 1 TB. But the 2 TB and 4 TB drives stand out a bit. We think it’s because WD has chosen to use 512 Gbit NAND in these, instead of 256 Gbit as in the other models. We have of course asked WD and unfortunately they refuse to share any information about this. It’s a shame that manufacturers aren’t more willing to share the details of these things.

Components and design

If we look a little closer at the device, we see that there are differences between the SN750 and SN700. We know they use the same controls but the SN750, which we tested here , has part number 20-82-007011 and the SN700 has 20-82-00705-A2. It looks like a newer revision of the controller is being used and this appears to be used by the SN730, which is an OEM version of the SN750.

SLC cache and heat

We’ve previously tested several devices that use the same controls, so there shouldn’t be any surprises. WD’s controller uses a static cache that provides significantly higher performance than TLC can normally deliver. A static SLC cache provides very consistent performance but is also significantly smaller than many others. With WD Black, a dynamic cache has been added, but that is not the case here.

The performance is around 2,500 MB/s for a couple of seconds. When the cache is exhausted, it switches to writing directly to the TLC. In this case, the TLC performance is really good, around 1700 MB/s. The reason could be that the SN700 uses BICS4 NAND. WD again doesn’t want to confirm this but it feels very likely.

Performance

The SN700 is not entirely unexpected at about the same performance level as the SN750, which is not a bad starting point at all. At the same time, this means that it is not much faster than the SN570 and the Samsung 980. These four devices are at about the same performance level in most of our tests. Client performance is slightly higher on the SN700, likely due to newer NAND flash. In the workstation test, it lands at about the same level as the previous SN750 and SN570. In terms of file transfers, the SN700 is a bit sharper and this is mainly due to the device’s very good writing performance to TLC.

Although the WD Red is primarily designed as a cache SSD for NAS, it can stand on its own without any problems. The SN700 is roughly at the same performance level as the fastest PCIe 3.0 drives. The absolute biggest difference is that this device has a significantly higher TBW value to work well as a cache for NAS.

Summary

The WD Red SN700 is more or less a WD SN750 using WD/SanDisk BICS4 NAND. However, it is not impossible that WD binned specific NAND chips to be able to give the Red SN700 significantly higher TBW than many other consumer SSDs. This is important for NAS devices that use SSDs as cache, to improve performance. Most NAS manufacturers recommend getting an enterprise-class SSD if you do very write-intensive operations on your NAS. Buying a WD Red SN700 can be a way to get away a little cheaper.

Performance-wise, we don’t have much to complain about and the drive is roughly on par with the WD Black SN750, which is still one of the fastest PCIe 3.0 drives on the market. Thanks to WD’s efficient controls, it is also one of the most power efficient and efficient drives on the market. There really isn’t much to complain about in terms of performance or efficiency. The SN700 also has the highest write performance to TLC that we have tested with any SSD in a long time. It’s even faster than the SN850 and 980 Pro.

The WD Red SN700 has one problem and that is the price tag. At the time of writing, an SN700 costs almost twice as much as an SN750. In such a situation, it may be more relevant to buy a larger SSD because you then automatically get more TBW. We therefore find it a bit difficult to see the point of the WD Red SN700 for the vast majority of consumers. If you have a NAS and you know you will be writing a lot to the cache, then the WD Red SN700 is a device you should consider.

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