unRAID

Source
Overview
Digital Media Storage Solutions
unRAID Server is an embedded Network Attached Storage server Operating System designed to boot from a USB Flash device and specifically designed for digital media storage:
Digital Video
Digital Music
Digital Images/Photos
Unique RAID System
unRAID Server employs a unique RAID technology which provides for great configuration flexibility:
Any combination of IDE and SATA hard drives may be used.
All the hard drives do not need to be the same size or speed.
Hard drives not being accessed may be spun down.
Can rebuild any single failed hard drive.
True Incremental Storage
Unlike other RAID systems, unRAID Server supports true incremental storage expansion. You can add capacity by adding more hard drives or by upgrading existing hard drives. This is a great way to make use of older, smaller hard drives you might have laying around.
For example, you might start out by installing one or two new high capacity hard drives along with some number of smaller hard drives you already own. Later, you might decide to replace one of the smaller drives, and unRAID Server will restore the data of the smaller drive onto the new drive, and then expand the file system to incorporate the full size of the new drive.
Better Fault Tolerance
Similar to other RAID systems, unRAID Server permits reconstruction of a single failed hard drive. However in the unlikely event of multiple hard drive failures, data loss would be isloated to only those hard drives which failed. In traditional RAID systems, multiple simultaneous hard drive failure results in complete data loss.
Network Attached Storage
unRAID Server is compatible with Windows Networking. Individual data disks appear as disk shares under My Network Places. In addition, unRAID Server provides a composite view of all your storage through the use of User shares.
User shares permit you to view your storage as if it were one large file system, even though each data disk has it’s own file system. This lets you define share names such as Movies, Video, Photos, etc. whose actual contents are spread out among multiple hard drives.
Installed On A USB Flash Storage Device
unRAID server is designed to be installed on, and boot from, a USB Flash Storage device. All configuration data is also kept on the Flash; the hard drives are only used to store user data.
Supports Multiple Hardware Platforms
unRAID Server is largely hardware independent. System builders: please visit the Hardware Compatibility page on the unRAID Wiki for the latest list of supported hardware.

 A more detailed introduction: Technology and Uses

 

Advantages of unRAID over similar products

No striping, so safer for multiple drive failures; parity protection, so resistant to single drive failure; flexible, can mix and match drive brands, sizes, and types, easily add additional drives, etc...

Each drive is an independent file system. An unRAID array can be thought of as a parity protected JBOD. If the array fails, the individual drives are still accessible, unlike traditional RAID arrays. Spin down can be controlled per drive, so a drive with rarely accessed files may stay off (spun down) for months, saving power costs, and possibly increasing its life. With standard striped RAID arrays, the entire array must be spun up or down, so generally stays spun up.

Some good threads about advantages/disadvantages of unRAID and similar products:

• http://lime-technology.com/forum/index.php?topic=1191
• http://lime-technology.com/forum/index.php?topic=2902, particularly this post, but read the whole thread
• http://lime-technology.com/forum/index.php?topic=2103.msg15834#msg15834

More threads about the advantages of unRAID in the unlikely event of multiple drive failures:

• "How Many Disks Can unRAID Lose?"
•  "Nightmare - 2 drive failure"

Disadvantages of unRAID compared to similar products

No striping. So, although it performs well, and better than many NAS solutions, is generally slower than a RAID 0, RAID 5, RAID 6, or RAID 10, etc. If performance is very important for an array you may be building, then one of the 4 RAID types just mentioned will be a better choice than unRAID. 

Is unRAID for me?
We unRAID users think so, of course. But read for yourself a few forum threads:

• "Is unRAID for me?"
• "How are you using unRAID Server?" - a small poll
• "Seems to me unRAID is NOT cheap" - excellent, very open and candid debate, Buffalo NAS vs unRAID
• more to come (when I find them)

Minimum System Requirements?
Intel compatible computer

• Motherboard and components compatible with unRAID software (based on Slackware), and Linux kernel 2.6.*
• 512MB of RAM (recommend 1GB or more depending on usage)
• USB flash drive
• can operate without video, monitor, or keyboard; does not use mouse
• see Hardware Compatibility for extensive hardware and compatibility information

How is unRAID licensed?
The unRAID Server software is available under 3 different licenses:

• unRAID Server Basic - FREE! - 3 drives (2 data, 1 parity)

Although the FAQ is good for answering specific questions, if you are browsing for general information about unRAID, why not check out the Best of the Forums. Categorized links are added often, so it pays to check it periodically. It's a great way to stay current with what is happening and being discussed in the unRAID world. 

See also

• Un-Official UnRAID Manual
• The Official unRAID Reference Manual
• Best of the Forums
• Troubleshooting Guide
• UnRAID Add Ons - for information related to add on scripts and tools, such as UnMENU
• unRAID forums
• UnRAID Wiki