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It should focus on easily recoverable data. This means that if I take any drive from the pool and mount it some place else, I would be able to read data from it. Also, if a drive from the pool fails, only data from that drive will be lost. Data from other drives would be unaffected.

I have already tried LVM. I lost a drive in the pool and was able to recover files from the other disks. However, not all of the recovered files were good. Some are too short/corrupted.

Which is why I'm looking for an alternative to LVM. Ideally, the solution would sit on top ext4-formatted disks (or any other filesystem), and drives will fill one by one. And if I want to share my drives (using NFS or Samba), I would just point it to the solution mount.

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closed as not constructive by Zoredache, ewwhite, pauska, Jacob, SvW Feb 26 '12 at 16:24

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I don't understand what you're trying to accomplish. Why would you want to move a disk to another location and read from it? –  ewwhite Feb 26 '12 at 7:02
    
Is this for your home computer, or some kind of professional setting? The short answer, is that there is almost nobody that actually wants anything like you describe, so it seems very unlikely that anyone has built it. –  Zoredache Feb 26 '12 at 7:21
    
It's just for a home setting. I would only remove a disk if it's failing. Otherwise, it would behave just like an LVM would do. Unfortunately, for LVM or RAID, just removing a disk is not possible without damaging the filesystem. I've searched Google for a similar system but I haven't found what I'm looking for. –  zang3tsu Feb 26 '12 at 9:57
    
BTW the only thing that comes close to doing this is a Drobo, and what it does is proprietary. –  Zoredache Feb 26 '12 at 10:08
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2 Answers

You would need to set up a raid-1 mirror to accomplish this.

You said you want to be able to mount the drive elsewhere. You cannot mount a drive that you just yanked out of an array. Even if the drives were ordered in an append configuration, the filesystem locates files by their offset from the start of the volume. So if you yank out a drive in the middle of the array and try to use it elsewhere, the start of the volume is no longer the same and files cant be found. So the only drive that you could remove and mount up elsewhere would be the first drive (again, assuming that the drives are in a serial append config). But then the machine you just pulled the drive from wouldnt work any more.

Ultimately this is just a very bad way to approach the situation. The proper way to handle being able to remove drives and access them elsewhere is a raid-1 array. It can be raid-1+0, raid-1+5, whatever, just has to be raid-1 to have 2 fully functional filesystems. (Though if you want to nit pick, a 2 drive raid-5, or a 4 drive raid-6 can also do this)

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I can't really use raid since my use case is gradual addition of hard disks. LVM is great for this, however, disk failure is problematic: when the virtual volume is back up (minus the failing drive and plus a new drive), some of the recovered files are too short/corrupted. –  zang3tsu Feb 26 '12 at 10:03
    
@zang3tsu You can add disks to a raid array without having to rebuild it. –  Patrick Feb 26 '12 at 10:14
    
Would it also work if the disks are of different sizes? –  zang3tsu Feb 26 '12 at 11:14
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Since you mentioned network access, you can give a try with a distributed network filesystem like GlusterFS, since it will store all the files in standard POSIX mounted filesystems from which data can be easily recovered.

http://download.gluster.com/pub/gluster/glusterfs/3.2/Documentation/AG/html/ch01.html

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Thanks, I'll look into it. –  zang3tsu Feb 26 '12 at 9:57
    
Hmm, it's great but it might be too much for a home setting. –  zang3tsu Feb 26 '12 at 11:15
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