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What I'm looking for

An easy way to join multiple disks into one drive. I which to be able to disconnect a disk without the other disks complaining, they should just display what data they have. Data on the removed disk would obviously be gone.

I don't care about performance as it's just storage.

What I've tried

  • RAID but that won't allow me to remove a disk and the entire thing will fail if one disk fails.
  • Dynamic disks is what I'm running now and it's almost what I want however you cannot remove or add a disk easily.
  • Symbolic links is not what I'm looking for.

Any suggestions?

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I can't think of any filesystem that won't throw a fit if a chunk of its space and files suddenly disappeared. The partition would also have to be dynamically resized, and filesystem metadata would have to be mirrored across all drives and automatically fall back to another one if the primary is unavailable. Unless you have a primary drive you will never remove, of course. And that doesn't even account for the fact that files on a single partition spamming multiple drives could easily be fragmented all over the place, meaning you'll be missing parts of files. –  Bob Apr 27 '12 at 18:35
    
RAID 5 does this, but you'll need 5 disks of equal size for that. –  Snæbjørn Apr 27 '12 at 18:38
    
RAID 5 requires a minimum of three: two for striped data and one for parity. As Lucas points out in his answer, RAID is not designed for disks being constantly removed. –  Bob Apr 27 '12 at 18:49
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Why do you think symbolic links aren't what you're looking for? Explain what you need that they don't provide. How about mount points or directory junctions? –  Ben Voigt Apr 27 '12 at 20:36

2 Answers 2

You have a bunch of possibilities, but if you want to be able to disconnect a disk and not lose data, I think you will have to use RAID.

The options would be:

  • RAID 1 (One disk can fail)
  • RAID 10 (one of the RAID 0 arrays may fail)
  • RAID 5 (1 disk can be removed)
  • RAID 6 (2 disks can fail)

But be warned, just disconnecting a disk for fun isn't really what RAID is built for. It's built to have reliability.

Bob's comment covers all the reasons not do this. So in the end the answer would be: There is no way to do this.

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That's kinda the point, being able to withstand disk failure doesn't mean they should be disconnected. Disconnecting and later reconnecting a disk in a RAID array will result in drastically reduced performance as it rebuilds the array (often takes my Windows install up to 30 mins to start compared to normal max 1 min if it's rebuilding the RAID 1 array). And worst case the controller makes a mistake and rebuilds the wrong disk... using outdated data/parity from the replaced disk... bye bye data! Not to mention you can't remove any disks until rebuilding is complete. –  Bob Apr 27 '12 at 18:47
    
You are right, updated my answer. –  Lucas Kauffman Apr 27 '12 at 18:50

It's not "easy", but consider a Drobo or a Synology NAS server. They each have their own RAID-like solutions that help with adding/removing drives.

Synology Hybrid Raid: http://forum.synology.com/wiki/index.php/What_is_Synology_Hybrid_RAID%3F
Drobo Beyond Raid: http://www.drobo.com/how-it-works/beyond-raid.php

Personally I prefer Synology as the "DiskStation" OS has literally 100s of features (AD/DHCP/CloudStorage/MySQL/etc)

Models range from a couple hundred dollars (home) to a few thousand (enterprise level) - but you can pickup a 4bay for ~$500.

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I'm under the impression that you need to give the system time (several hours?) to move data around before you can remove a disk. –  Ben Voigt Apr 27 '12 at 20:38
    
Before you can move disks safely yes. You can always remove a disk, but if you are only setup for 1 disk redundancy and you remove a disk before allowing it time to reorganize a drive could fail and you lose data. You could always setup for 2 disk redundancy. –  csauve Apr 27 '12 at 20:42
    
The main thing is you actually are able to add/remove disks. Normal RAID is not very good at this. –  csauve Apr 27 '12 at 20:43

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