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I have an HDD partitioned with one partition used for media files, mounted somewhere on my system (which is a Debian Wheezy box). I would like to expand the space available for files in my mount directory - using an additional HDD, but without using another folder or a subfolder.

I understand LVM is an option - but for that I need to make the transition without moving or backing up any files (these aren't critical files, but obviously I don't want them gone). Can this be done?

Also, a better option would be if the partitions on the old and new disk simply both 'contributed' space to the same place, so that individual files would be written either entirely on one disk or entirely on the second, and that if I took out the second disk it would just be usable as-is without LVM. Is that possible?

Update: I tried lvmify, but it blurted an error and didn't work.

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up vote 1 down vote accepted

LVM is basically the only easy way of doing it. You will have to move data around.

The only other way and, it would require additional hard drives, is a hardware or software RAID. Obviously hardware is faster and uses no CPU, but can be expensive. However you can add as many identical capacity hard drives as you have connectors for with this method. RAID 5 would allow 1 hdd to fail without losing data and RAID 6 would allow 2 hdd to fail. RAID 5 requires 3 hard drives minimum and RAID 6 requires 4.

I did the whole LVM thing for a while until I had a hard drive failure and released I had no redundancy with LVM. If you use a LVM make sure you have reliable backup method. For approx $10 a month you can use CrashPlan on linux.

Make sure you have a backup and then read this:

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Why do think aufs is not an option? – einpoklum Apr 2 '13 at 6:36 Has a disturbing note: "Aufs was rejected. Let's give it up." According to Christoph Hellwig, linux rejects all union-type filesystems but UnionMount. I have to admit I don't know much about the file system itself, and would have to research it. – cybernard Apr 3 '13 at 5:28

LVM will do what you want, but sadly, not without some form of moving data around; take a look at this discussion of union mounts for something that may be usable for what you are looking to do.

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