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. What you want: ZeusRAM 8GB ($300- $2000 on ebay varies by availability)
  2. Money is no option: Intel DC P3700 400GB ($400-750 on ebay varies by availability)
  3. Slightly less expensive: Intel DC P3600 400GB ($350-550 on ebay varies by availability)
  4. SAS option: HGST SLC or MLC 100GB, 200GB or 400GB drives ($75 to 300 on ebay)
  5. SATA options: Intel DC S3700 series 100GB, 200GB or 400GB drives ($100 to $250 on ebay)

The key here is that you want 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.

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.

Intel DC P3700 400GB
Intel DC P3700 400GB

The Intel DC P3700 400GB drive can 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 con 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).

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 over provisioned 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 these 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.