Building an unRAID Server

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Important Warning! This wiki page has not been updated for v6! Some information is out-of-date!


unRAID is a file server system, based upon the Slackware distribution of Linux.

unRAID allows you to build an 'array' of hard drives and share those drives across the local network for all users to access the files on those drives. In order to help combat physical drive failure, unRAID allows for the inclusion of a parity drive, which is used to contain parity bit information for all of the other data drives. This information can be used to rebuild the data on any drive if it has to be replaced (either for an upgrade or because it died).

The benefits of unRAID versus other systems such as FreeNAS are:

  • Ability to have different sized drives in the array (RAID normally requires you to have all drives in the system be of the same physical size)
  • Ability to dynamically add drives to the array as they are acquired - most RAID arrays are very sensitive to "growing" the array and the operation typically involves a full backup before attempting to grow the array. If you've got 5 TB of data, this likely isn't something you're going to attempt!
  • Non-striping of the data or parity - normally, the data and parity information in a RAID is striped across the disks, meaning portions of each file are stored on various drives. In unRAID, files are stored contiguously on a single drive. This means that if there is a catastrophic problem (e.g. multiple drives fail), you can likely retrieve the information from a single disk.

Of course there are some drawbacks to unRAID:

  • Some limitations in hardware support - see the Hardware Compatibility page
  • It's not free (for more than 3 drives) or open source
  • Since the data is not "striped" across multiple drives, read performance is limited to the speed of the individual drive. In most RAID implementations, data can be read much faster than an individual drive's performance because various drives are accessed simultaneously, thus aggregating the read performance.


Main article: Designing an unRAID server - general issues to consider when choosing hardware components
Main article: Hardware Compatibility - for up-to-date hardware recommendations
  • CPU: Basically anything. Single core CPUs are fine, though multi-core CPUs can be useful for certain unRAID add-ons.
  • Memory (RAM): Minimum 512 MB, but 1-2 GB is recommended. 4+ GB is recommended for certain unRAID add-ons.
  • Video card: Use the onboard video if possible, if not, then look for the cheapest card you can get off eBay, preferably a PCI-based video card (you will want to save your faster PCIe ports for SATA controller cards).
  • Hard drives: either PATA or SATA drives of your choice. Remember though, that the largest will be used for parity, and those old drives you've got laying around probably will die as soon as you put something important on them! SATA drives will be faster and also will be easier to route cables since their cables are much smaller. Also remember that they tend to take different power supply connections, so plan accordingly (do you need adapters?).
  • Motherboard: You will need a newer motherboard that allows you to boot from a USB stick. Some of the oldest boards do not. Look for one with at least 6 SATA ports, Gigabit Ethernet (GigE), and onboard video. You will need to be careful here if you choose something else, to make sure that the onboard devices are supported. Support for these has increased with each unRAID release, but it still boils down to:
  • Onboard SATA: Intel ICHx, nVidia nForce, AMD or ATI SB600+, possibly some VIA chipsets? (and a couple more I'm sure)
  • Onboard LAN (preferably gigabit only): Intel, Marvell, some VIA (slow) and Realtek
  • PCI or PCIe SATA Cards: The Promise TX4 is the most widely trusted PCI SATA controller card, but it is slow by today's standards. Avoid using the PCI bus at all if possible. Look for a SATA controller card that uses PCIe. Note that PCI-X is different from PCIe. You will not be able to use PCI-X unless your motherboard specifically supports it.
  • USB Memory Stick: at least 512 MB, though 1-2 GB is cheap and readily available.
  • Power Supply (PSU): If you're going to be building a server that's powered on for long periods, and that has a lot of hard drives, then you will need a good quality power supply, so don't skimp on this part! Look for a power supply that has a single 12+ volt rail and that is 80plus efficient or better. Also make sure that your PSU is compatible with your motherboard, since some motherboards require 8 pin power cables instead of the standard 4 pin power cables. Reputable brands are Corsair, Seasonic, and Antec Earthwatts.
  • Case: Almost any case will do for a small array. Bigger arrays will need more thought. You will need to think about ventilation. Hard drives get hot and they are very susceptible to heat (most are rated to 55*C). There are 5-in-3 drive cages and backplanes that allow for 5 hard drives to be placed into 3 5.25" drive bays. Consider potential heat issues with drives that close together (though many backplanes have dedicated fans), and also the extra expense of these drive cages. Fans and airflow are very important. Please see the UnRAID Topical Index, Fans section.


Fitting the components together is usually straightforward, and requires little prior knowledge or experience. A typical assembly would involve the following steps:

  1. Take the sides off the case.
  2. Attach the power supply inside the case. Some users recommend that this is done upside down, so that the fan opening is inside the case.
  3. Install the 9 standoff screws to the ‘floor’ of the case. Look at the motherboard to identify where to place them – they need to correspond with the motherboard holes that have a ‘star’ pattern of solder.
  4. Put the metal backing panel into the case. This makes the keyboard/mouse/USB/network/etc ports look pretty, and blocks a source of air leaks that may make it hard to get good airflow through the server.
  5. With the motherboard outside of the case, install the processor. Lift the arm on the socket, align the processor and gently place it in (align the pins - one corner doesn't have a pin, so make those match. Close the socket with the arm and latch it.
  6. Align the CPU heat sink and attach to the socket. Heat sinks are often supplied with thermal paste already applied, so there is no need to add separately. However if it is NOT already applied, you MUST apply it yourself! NEVER use a CPU and heat sink without thermal paste or thermal pad.
  7. Install the RAM.
  8. Drop the motherboard into the case and attach with nine rounded head screws. Tighten the screws in a star pattern, little by little – do not completely tighten one screw before putting in any others.
  9. Connect the rear fan and processor fan to the motherboard.
  10. Connect the front panel cables to their respective connectors on the motherboard. These wires are small and don't lock into place. Certain plugs are mandatory – PWR (power switch) and RST (reset switch), for example. Other plugs, such as PWR_LED and HDD_LED, are optional, although PWR_LED will be useful, showing when the server is on. unRAID does not make use of audio ports, so plugging in the front panel audio is also optional.
  11. Connect the power cables to the motherboard. Two are usually required: one big fat one (24 or 20 pin) and small one (4 or 8 pin).
  12. Attach a power cable to each SATA hard drive.
  13. Connect SATA cables from the motherboard to the drives.
  14. Connect to the network.
  15. Connect a monitor and keyboard (usually required only for the first boot).

Prepare the USB Flash drive

Formatting the USB Flash drive and installing the unRAID distribution files on it

Main article: USB Flash Drive Preparation
Main section: Instructions
Troubleshooting section: If the Flash will not boot...

On any Windows or Linux PC:

  • Insert the memory stick and format it using FAT or FAT32, and enter UNRAID as the label.
  • Get syslinux.exe from
  • Run syslinux -ma x: (where x: is the drive letter for your memory stick) **Note for Vista and Windows 7 users: To run it, right-click the file and choose 'Run as administrator'**
  • Download the distribution you want from and extract all the files to the memory stick, preserving the folder structure (there should be a config folder with files in it)
  • Set the volume name of the memory stick to UNRAID (if you forgot in the first step above)
  • Safely eject the memory stick from your computer
  • Many users have had problems with these seemingly simple steps, because unfortunately, there are numerous compatibility issues between various motherboards and flash drives. The USB Flash Drive Preparation page is a comprehensive guide to USB flash preparation, with many tips and alternative steps to try.

Starting the server

Verifying the BIOS settings, the memory, and the networking

Main article: USB Flash Drive Preparation
Main section: Booting unRAID Server
  1. Before plugging in the USB Flash drive, boot the machine and enter the BIOS settings screens, sometimes known as the CMOS settings. This is often done by pressing the <Del> or <Delete> key during the early part of the boot process, but may instead require the <F2> key, or the <F1> key, or the <F10> key, or some other key or combination of keys. Please check your motherboard manual.
  2. Check that all of the drives are recognized by the BIOS and/or add on controllers. However there are exceptions where some drives and controllers won't appear in the BIOS, but will still be available to unRAID later in the boot process.
  3. Power down the server, install the USB stick, reboot, and again go into the BIOS settings.
  4. Configure the BIOS so that the motherboard uses the USB Flash drive as the boot device. The option is often labeled as ‘USB-HDD’ or ‘forced FDD’, but there are other choices that may also work.
  5. Confirm that you can boot from the USB stick - you should get a boot menu with at least 2 choices, unRAID and memtest.
  6. Boot into memtest and let it run for 2 complete cycles. Later you might want to come back and run it overnight, but 2 cycles should give you pretty good confidence that you don't have any memory errors.
  7. Press the <Esc> key to reboot, and this time let unRAID start.

You will first see a command line prompt on the monitor. Type root and press the <Enter> key, no password will be needed. (Later, you may want to set a root password on the Users tab of the unRAID Web Management pages.)

Verify that you have an IP address by typing ifconfig and pressing the <Enter> key. You should get an output similar to this:

 eth0      Link encap:Ethernet  HWaddr 00:1A:4D:27:13:8A
           inet addr:  Bcast:  Mask:
           RX packets:16261 errors:0 dropped:0 overruns:0 frame:0
           TX packets:2850 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:1067783 (1.0 MiB)  TX bytes:1193253 (1.1 MiB)
           Interrupt:21 Base address:0xa000
 lo        Link encap:Local Loopback
           inet addr:  Mask:
           UP LOOPBACK RUNNING  MTU:16436  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

On a computer that is on the same network, open a browser and go to:


This should take you to the unRAID Web Management 'Main' page, where almost all unRAID setup and management of your server is handled.

If you are using a Mac, you may initially need to use your server's IP address instead of 'tower'. For further instruction, please see the FAQ, Apple Mac Questions section.

Configuring and starting the array

Preparing the drives and setting up the array

  1. Go to http://tower
  2. From the Main Page, select Devices from the menu.
  3. In your Disk devices, verify that all the hard drives are showing up, by clicking on any of the drive dropdown boxes. If not, then you either have connected them to an unsupported device, or you forgot to connect them, or there is a loose connection in the power or data cables.
  4. The parity drive must be the largest, or equal to the largest data drive. You can assign it now, or do it later.
  5. Assign the other drives to be data disks, in whatever order you wish, and to whatever slot you decide.
  6. Go back to the Main screen and Start the array. If you have assigned the parity drive, then a parity sync will start.
  7. Copy your data from your workstations / existing servers to the data disks.
  8. If you have assigned the parity drive, then run a manual parity check - make sure it completes with 0 sync errors.
  9. Run smartctl on each drive to make sure that no serious errors have developed.

There are two optional but recommended steps that may alter this order:

  • Before Step 1, install the Preclear script and run it on each of your drives. (Several of these can be run in parallel, as these tests take time). This script really runs the drives through their paces, and if they have any SMART errors they will likely be detected before you assign them to your array. For more information, see the #Preclear Disk addon.
  • If you have a lot of data to transfer over, you can copy it faster if the parity drive has not been installed yet. But make sure you install and build parity before you delete backups of anything you transfer to the array.


By default, unRAID creates a share for each disk in the array (eg. \\tower\disk1, \\tower\disk2, etc). However, unRAID also supports the concept of User Shares. You can create folders in each of the disk shares, and then a user folder will "aggregate" all of the content from each share into one share with that folder name. So, if you have \\tower\disk1\DVD and \\tower\disk2\DVD, a user share can be created for \\tower\DVD. To turn on user shares, go to the Shares menu item. Select an option from the User Shares dropdown. If you want the shares to be read-only, select "Export read-only."


You can set passwords for "root" and any other user you define. You can limit specific shares to specific users, and restrict specific users from write permission while granting write permission to others. This is all configured per share on the Share page. Basic "root" security is available on all versions of unRAID, but User Security is only available with an unRAID Plus or Pro license. All security settings can be changed on the Security page. To delete a user, delete the user's name and password and press Save.

Helpful Info

You can Telnet into the server, either using the built in Telnet app or PuTTY (a free download). Once you Telnet in (or use the console on the server), you can run important Linux commands such as:

  • top: similar to the task manager in Windows, press q to exit
  • df -h: tells you how much space is left on your drives
  • shutdown -h now: tells the system to shut down in an unclean way, right now (not recommended!)
  • shutdown -r now: tells the system to reboot in an unclean way, right now (not recommended!)
  • ifconfig: tells the IP configuration (similar to ipconfig in windows)
  • tail -n # <file>: display the last # lines of <file>
  • ls: similar to dir in DOS
  • du -s <directory>: how big a certain directory is
  • mount: shows you the mounted file systems
  • smbmount //server/share directory: mount a Windows (or Samba) share to the given directory -- this is useful for copying files from one server to the other (will be faster than copying in Windows Explorer)
  • There are more console commands listed on the Console wiki page, and much more about consoles and using Linux in the unRAID Console and Addon Questions section of the FAQ.