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I want to use Ubuntu Server on a computer which I want to use for my backups. I would like to be able to add extra disk space if that would be required in the future. Basically, I like what the Drobo does, however, I don't like that it uses a proprietary file system. Which means that I totally depend on them if it breaks.

So I have looked into mdadm for RAID 5 + LVM. However, that will not use all disk space if new disk are larger than the old ones. (LVM for the snapshots) I think ZFS could do the trick, however, that is unsupported on Linux. BtrFS is a bit too young to trust my files to, it is my backup after all, I want stuff to be safe there.

Another reason for me to want an ubuntu machine instead of a NAS, is that I want to run other stuff on it as well, like Django, mythtv backend and mail server.

So what options do I have if I want my files to be stored in a redundant fashion, and to be able to take snapshots of these backups as well?

I'm still in the research phase, so I am open for suggestions. :)

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Have you looked into greyhole? – endolith Jan 20 at 21:56

You can use RAID 1 + LVM on top When need more space - add 2 more disks, create another RAID 1 with them and add it to the existing LVM

LVM also supports snapshots

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The downside of that is that it requires a lot more disks. Another solution which is out there is unRAID: However that would not allow me to run a mythtv backend on it... – user9713 Jan 27 '11 at 15:12
with RAID 5 try to add say 2 more disks without rebuilding the raid - good luck. Also needs expensive controller. With RAID 5 you cannot mix disks with different sizes – jet Jan 27 '11 at 15:35
My biggest problem with will be that most atom boards have only 4 SATA ports at most. So that will leave me with two raid 1 arrays + lvm. As explained in the question, I know it is possible to mix different sizes in RAID5, when using partitions of the same size. However, I will not be able to use all space (in RAID), I could use the extra space as non raid (losing redundancy). – user9713 Jan 28 '11 at 7:49
+1, disks are cheap, and physically shrinking all the time. This solution also means your data is super redundant. Eventually (soon I hope), BTRFS is the way to do this, but not today. – SpamapS Jan 28 '11 at 18:04

MD has a container mode which is a "RAID of RAIDs". As you added more disks, depending on whether they could fit into an existing raidset, you could create a new raidset and add that to the container. I bet drobo does the same thing.

From the man page.

   CONTAINER  is  different again.  A CONTAINER is a collection of devices
   that are managed as a set.  This is similar to the set of devices  con‐
   nected to a hardware RAID controller.  The set of devices may contain a
   number of different RAID arrays each utilising some  (or  all)  of  the
   blocks  from  a  number  of  the  devices in the set.  For example, two
   devices in a 5-device set might form a RAID1 using the  whole  devices.
   The  remaining  three  might  have  a RAID5 over the first half of each
   device, and a RAID0 over the second half.

   With a CONTAINER, there is one set of metadata that  describes  all  of
   the arrays in the container.  So when mdadm creates a CONTAINER device,
   the device just represents the metadata.  Other  normal  arrays  (RAID1
   etc) can be created inside the container.

You also may be able to convert a RAID 1 MD array into a RAID 5. See,

Experiment with it and let us know how it turns out.

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