5. Cache Options
Overview
Unraid is going to be the most common choice for OS. In that case, it makes sense to have a decent size SSD to store your appdata and to be used as a write cache. This improves file transfer speed to your server immensely. Typically these files will be moved off of the cache drive and onto the array daily (at minimum), so keep that in mind when selecting a size. Smaller SSDs can be used as “unassigned” drives, which are neither part of the array or part of the cache. Unassigned drives can be used as VM data stores, file unpacking drives, or whatever you want really.
With the current Unraid beta release (v6.9.0-rc2 as of writing), you can have multiple cache pools that can be assigned to different shares. Personally, I take advantage of this by using RAID1 15k RPM HDDs for my large file ingest. It can easily write at over gigabit speeds with large video files, but it not as fast as a SSD for smaller files. In that case, I use my SSD cache. Offloading unpacking and large file ingest to a hard drive cache will greatly extend your SSD’s life span.
SSD Options
| Brand | Model (link) | Capacaity | Interface | Price/TB | Expected Price |
|---|---|---|---|---|---|
| Intel | SSD DC P3600 | 1.2TB | U.2 NVMe | $103.30/TB | $123.97 |
| Intel | SSD DC P3605 | 1.6TB | PCIe 3.0x4 NVMe | $103.71/TB | $165.95 |
| Intel | SSD DC P4500 | 2TB | U.2 NVMe | $99.50/TB | $199.00 |
| ADATA | SU720 | 1TB | 2.5" SATA | $89.99/TB | $89.99 |
| ADATA | SU720 | 500GB | 2.5" SATA | $99.98/TB | $49.99 |
| Sun/Oracle | F80 7069200 | 4x200GB | PCIe 2.0x8 | $125.00/TB | $100.00 |
Fast HDD options
Check out the list in the forum post below. Fast 2.5" SAS HDDs are available for less than $10/300GB or $18/900GB.