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I want to make a owncloud server in the raspberry and previously I want to make a Raid of my HD to avoid losses.

I have a 3TB external HD with 2 partitions of the same size and I want to use:

  • Partition 1 (1.35TB) -> To store the data
  • Partition 2 (1.35TB) -> To mirror the first partition.

I try to find something about this, but I can't because all the Raid tutorials are about mirroring all partitions of the first disk into the second disk, so I don't know if can be used only one disk to do it. All the info that I found says that minimum need 2 disk, is this true?

Maybe someone have done this before and can advice me.

  • Doing this on a single drive provides minimal if any protection against data loss or corruption. Also by definition this is not RAID. The RA in raid stands for redundant array. You need at least two drives. You may want to read this first en.wikipedia.org/wiki/RAID – Steve Robillard Mar 2 '16 at 11:38
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    Now that you answer this question I realized how stupid was, due if the hard disk is broken, is broken the whole hard disk. I'm going to find another hard disk to do it. Thank for open my eyes and sorry for the question. – CapAm Mar 2 '16 at 11:40
  • It seems to me that a good backup scheme would be easier to implement than raid. Especially since the Drives are likely going to be connected to the Pi via USB, and because the Pi's USB ports share bandwidth with the Ethernet port, you are unlikely to see any performance improvement from a raid array. – Steve Robillard Mar 2 '16 at 11:45
  • @UKAndroid I used to work in data restoring lab, and your schema is not a nonsense : it will help you in case of local disk surface error( in my practice it was >60% cases). You will be able to restore all your data or a way bigger part of it rather than not using RAID1(mirror) for a single drive. So keep it in mind – Alexey Vesnin Mar 2 '16 at 14:44
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True. You need at least 2 physical disks.

Pointless. The point of a RAID 1 array is to have two identical copies of the same data over two disks so if one fails, the data is fine unless you're really unlucky and both die at the same time.

Plain stupid (no offense :D). When the drive fails, it will take out all your data. No point in doing a RAID-1 then. Also, you essentially halved your storage capacity since, as mentioned, you need to have two exact copies of the same data. It will also be slow since it needs to write data twice. I'm aware you're aware of the capacity halving issue but there's also the speed factor.

Cumbersome. You need to hack the kernel to make it recognize your drive partitions as two drives.

Utterly pointless. I'll say it again. The point of a RAID-1 array is to have two copies in two drives (2 drives) so if one fails, the other has a copy. If you use only one disk, the essence of RAID-1 itself is undermined. You're better off using all of the disk's capacity.

The only benefit I can think of is that if there's a disk head crash, the other partition not covered by the damage will hold a perfect copy of the data. The problem is that you need to send it to a data recovery company since, as mentioned, the disk head literally crashed and scraped the platters.

In short, you won't avoid losses.

In shorter short, it's possible, it's superbly practical, and you should totally do it (sarcastic tone).

  • While I agree, it's a terrible idea (no actual redundancy, slower, etc. etc. etc.), wouldn't it be possible to do with mdadm without modifying the kernel? You can build a software raid based on the partition instead of the physical disk using mdadm. That said, I haven't actually tried it, so it may prevent you from doing this. wiki.archlinux.org/index.php/RAID for more info. – Ficertyn Mar 2 '16 at 15:51
  • @UnSined Interesting point. I haven't tried it either. I'll look into it when I have spare time (hint: I have a lot of spare time). – Gene Dela Rosa Mar 3 '16 at 8:21
  • I have since learned more, and it does make a bit of sense. Data redundancy on the same disk, in case of software errors. I'll make edits to this in due time. – Gene Dela Rosa May 14 at 10:36

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