Top Picks for FreeNAS ZIL/ SLOG Drives

FreeNAS is a FreeBSD based storage platform that utilizes ZFS. The fact that it uses a thoroughly enterprise file system and it is free means that it is extremely popular among IT professionals who are on constrained budgets. At STH we test hundreds of hardware combinations each year. From this experience, we are going to keep a running log of the best FreeNAS drives. We are going to focus this guide on FreeNAS servers with under 30 storage devices and will periodically update the listing.

Like most ZFS systems, the real speed comes from caching. ZFS can take advantage of a fast write cache for the ZFS Intent Log or Separate ZFS Intent Log (SLOG). Here our are our top picks for FreeNAS ZIL/ SLOG drives.

FreeNAS ZIL/ SLOG Devices

The ZIL/ SLOG device in a ZFS system is meant to be a temporary write cache. As such, we would expect that the drives are:

  1. General Purpose Top Pick: Intel Optane 900P 280GB


This has plenty of write endurance for most applications with 10 DWPD rating. The low latency and low QD performance of the Intel Optane 900P and 905P drives are excellent and price wise they are very attractive. If you want something bigger, we suggest the 480GB Intel Optane 905P

2. Current Top Pick for Heavy Usage: Intel Optane P4800X 375GB (or 175GB if you can find them):
3. Solid backup option: Intel DC P3700 400GB ($300-500 on ebay varies by availability)

The key here is that you still power loss protection, reliability, low latency, the ability to withstand a heavy write workload and ease of integration. While you may be tempted to get a NVMe m.2 SSD, the options with power loss protection are very hard to find as of this writing. You also do not need a huge SSD and can generally over provision a lower write endurance SSD significantly. 400GB is too large but some folks like having ample NAND on the devices.

Intel Optane 905p Big
Intel Optane 905p Big

You will notice that Intel Optane drives are featured prominently. When we tested the Intel Optane storage against traditional NAND, these were a clear winner. See Exploring the Best ZFS ZIL SLOG SSD with Intel Optane and NAND. The Intel 900p and 905p SSDs are the consumer versions of Optane, yet they still feature awesome performance and 10DWPD endurance, similar to an Intel DC P3700 NAND SSD.

Our top pick if money is no object, or if the anticipated workload involves heavy writes, is the Intel Optane based Intel DC P4800X 375GB. You may be tempted for a larger drive but this is too large. We have seen 175GB versions of the drive pop up as testing samples, and those are also plenty big for a ZIL device. Using Intel Optane memory gives low latency and high bandwidth at low queue depths with is exactly what we want. If your job depends on it, and you have a budget for it, get the Intel DC P4800X.

Intel DC P3700 400GB
Intel DC P3700 400GB

For legacy systems, the Intel DC P3700 400GB drive can still perform very well and can often be found at reasonably low prices. By utilizing PCIe and NVMe it is one of the better options on the market and receives high marks for write endurance, reliability and ease of integration. The Intel DC P3600 400GB is significantly slower than 800GB and larger models in the P3600 family but it can often be found at sub $1/ GB prices and is still an excellent drive. NVMe drives are nice because integration with FreeNAS is extraordinarily simple (e.g. Plug-and-Play).

Previous Generation/ Niche Options

There are a number of options that are still valid, especially for smaller FreeNAS servers without an open PCIe x4 slot or port for an NVMe SSD, or where power consumption precludes using a higher-end NVMe drive. Another use case is in 1GbE servers where there is simply no need for higher levels of performance. For these, we have our previous generation/ niche options.

  1. Slightly less expensive: Intel DC P3600 400GB ($250-350 on ebay varies by availability)


2. SAS option: HGST SLC or MLC 100GB, 200GB or 400GB drives ($75 to 300 on ebay)

3. The “classic”: ZeusRAM 8GB ($300- $2000 on ebay varies by availability)

4. SATA options: Intel DC S3700 series 100GB, 200GB or 400GB drives ($100 to $250 on ebay)

For most FreeNAS servers, the Intel DC P3600 still has plenty of endurance. These are higher-capacity NVMe drives and were deployed in large quantities. If you are looking for an inexpensive NVMe SSD for a ZIL/ SLOG device, this is a well-built option.

The ZeusRAM 8TB uses DDR3 RAM and has a power loss protection circuit to keep data safe in the event of an emergency. The 8GB capacity is more than ample and these drives integrate very easily in systems since they are standard SAS drives. The DDRDrive product would be a good option but it is intended for Solaris based ZFS systems so integration with FreeNAS is not there. With that said, because the SAS interface of the ZeusRAM is still a limitation if you have a smaller SATA only system. This was a popular product before NVMe SSDs came out. We would not pay a premium to a quality NVMe SSD for these.

Perhaps easier to use is the Intel DC S3700 series. Unlike the S3500 or S3610 drives, the S3700 100GB drive still performs well. The Intel S3700 drives are a gold standard in SSD reliability and they have firmware and write endurance optimized for heavy write workloads. Given used pricing, these are the dives to get if you are out of PCIe lanes. Likewise, the HGST 100, 200 and 400GB drives come in highly overprovisioned SLC and eMLC flavors. They used Intel NAND and controllers but were designed with HGST SAS2 / SAS3 interfaces and are built like tanks. If you go this route, skip the HGST-STEC drives as those generally have lower performance.

Hitachi HUSSL4020ASS600 200GB SLC SSD
Hitachi HUSSL4020ASS600 200GB SLC SSD

Beyond the above, there are many options available for ZIL devices. At this point, we suggest SSD only. Old articles may discuss 15K rpm disks but there is no point to be using that old architecture anymore. Ensure that you use reliable drives with power loss protection. There is no need to get a 800GB 7+ DWPD drive, especially for smaller systems. We have seen 800GB ZIL drives in 4x 6TB systems used to serve media files and that is ridiculous. There are many ZFS systems that will work well without a ZIL and it is easy to hear “you need write endurance and power loss protection” and overspend as a result.

You can see more of our FreeNAS Buyer’s Guides here.

Last updated 2019/9/26