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I'm building a media server on a budget. Currently, the design is to have four 500GB disks in a JBOD-type format giving me one large 2TB store. The problem is if any disk fails, I lose the whole array's data. I'd like to avoid dedicating a disk to parity if possible, so I need to cope with some loss of data being a potential problem.

Most of my media files (~95%) are rips from blu-rays and DVDs of mine. It's a lot of work to re-rip the files, but it's not the end of the world if I only lose some of the files. Just inconvenient.

I'd like to set up a filesystem where I can tolerate 25% loss of media data and have the rest still usable. The OS can be on a separate disk. Aside from creating four independent disks (with their own filesystem), which I'd like to avoid due to the complexity, is there any filesystem or design/configuration that will suit my needs? I plan to use FreeNAS to serve the files across the network.

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    RAID 1 allows for 25% disk failure. This means 1 of 3 drives can fail and the RAID will still work. RAID 2 allows for a drive failure and bit rot. There are other choice of course. Of course with a RAID setup you lose some of the storage space.
    – Ramhound
    May 3, 2013 at 17:47
  • @Ramhound What? 1/3 is 33%, not 25%, and a RAID 1 controller that's worth what you paid for it won't lose data until every disk in the array has failed without replacement. And I've never even seen a controller that implemented RAID 2. Do you mean RAID 5, perhaps? If so, you should probably mention that two failed disks in a RAID 5 array will cost you everything you had stored on it.
    – Aaron Miller
    May 3, 2013 at 17:55
  • @AaronMiller - I typed 3 and I meant 4. I actually do mean RAID 2.
    – Ramhound
    May 3, 2013 at 18:10
  • The idea was to have an array which gave me the highest disk capacity but which tolerated the loss of data. I would have selected a RAID, but I would lose one drive for parity, which I'd like to avoid, if possible.
    – Thomas O
    May 3, 2013 at 18:12
  • @ThomasO If you're looking for an array which both stripes across disks (i.e. can present several smaller disks as one larger one), and offers redundancy (i.e. doesn't lose everything when one disk fails), then parity is a fact of life; if you're looking for an array that doesn't die until two disks fail without replacement, then I'd recommend RAID-5 with one parity disk, which would give 1.5TB space out of four 0.5TB disks.
    – Aaron Miller
    May 3, 2013 at 18:20

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When I first read the title of your question I thought it was a bit ridiculous given that redundant is usually in conflict with loss of data. As I read your description I realized that it was what I do on my home file server. Windows Home Server and DriverBender allow you to have a group of drives appear as a single volume. Then some of the folders can be marked for duplication and others not. My photos are duplicated across drives but movies are not.

Windows Storage Spaces also can allow this level of grouping and selective duplication but others have reported issues (see here)

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If you are going to use FreeNAS then why not just use ZFS. It is the simplest way at that point. I have a media center that I started in 2008 and have been slowly expanding it. I started with external USB drives that were setup in Raid1 and then moved to NAS drives that backed up to the USB drives. I finally moved last year to a dedicated file server running FreeNAS and utilizing ZFS. I now have the ability to dynamically grown the amount of storage necessary using storage pools and in some cases ZFS is better protects your data then software or hardware Raid. I currently have about 6TB in total storage and utilize about 80% of it. If I need to increase this I just buy a bigger drive and replace the smallest one or simply add it in. It will add the capacity to the storage pool and presto/chango I have more space.

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