Intro to Unraid
Unraid, an operating system for Network Attached Storage (NAS) servers, is a popular choice for beginners and veterans alike. It offers an easy to use GUI that allows users to easily extend the base OS with various plugins and apps. It is also a very flexible system when it comes to hardware requirements, lightweight enough to run on low end or low powered systems, yet can take full advantage of the latest hardware. Its method of handling storage is also extremely flexible, allowing users to add and remove disks at any time with ease.
Unraid, hinted at by its name, is not a RAID solution. It has three main storage types out of the box: the array, where data is stored; the parity disk(s), which offer protection against drive failure; and the cache, which allows data to be written quickly, then later moved into the array.
The array in Unraid is basically what is known as JBOD, or Just a Bunch Of Disks, in the world of pooled file systems. This means that there is no requirement that the drives be the same size or added at the same time. The array can consist of up to 28 data disks with the Pro license. These disks can be any size and can be added and removed whenever necessary.
The parity disk (or disks, Unraid supports up to 2 parity disks) gives the user protection against drive failure. With a single parity disk, you can have one array drive fail without loss of data. With dual parity, you can have two array disks fail (or one array and one parity). Once parity has been calculated, if a drive fails, you simply replace the failed drive with another drive of equal or greater size and Unraid will automatically rebuild the missing data. The only requirement of a parity disk is that it must be equal to or greater in capacity than the largest disk in the array. Unraid’s parity is calculated in real time, as data is written to the array, so it’s always up to date and ready to be used to rebuild data.
The cache can consist of one or more (up to 24 on the pro license) disks. If you have a cache disk enabled and it has sufficient free space, writes to the array are written first to the cache disk, then later when a program called ‘mover’ is run, the data is moved from the cache to the array. SSDs are often chosen for a cache drive due to their extremely fast write speeds compared to HDDs, though even a HDD set as cache can help speed writes to the array. Since Unraid calculates parity on the fly, writes directly into the array aren’t as quick as writing directly to a single hard drive. Writing to the cache drive, which isn’t protected by parity should use the maximum write speed of the device.
There are two additional types of storage devices used in Unraid: the OS drive and unassigned devices. The OS must be installed to a USB flash drive. Each time Unraid boots, the contents of the flash drive are copied in RAM, where it runs until the next shutdown. It’s recommended to use a quality flash drive for the OS.
The final storage type, an unassigned device, isn’t built into the base OS but is available as a plugin. An unassigned device is simply a drive that is mounted and accessible that isn’t one of the other types of storage described here. It’s most commonly used to access flash drives and external hard drives, though there are some other, more advanced uses that we’ll cover in a later article.
The only downside to Unraid, in most new users’ eyes, is the licensing cost. Unlike many of the other popular NAS operating systems, Unraid is not free. Licenses start at $59 and go up to $129; the more expensive licenses simply allow you to use more drives. It does have a free 30 day trial, however, allowing you to try it out and see if it’s right for you.