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I plan to build a Linux (Ubuntu 10.04) home file server soon with 3-5 x 2TB hard drives in RAID 5 software raid but I'm not experienced with setting up RAIDs.

Should I include the actual Linux host in that RAID setup or should I use a separate drive (I'll have an SSD lying around soon) and what are the caveats to this?

If and when I need to reinstall the host OS, will it be able to use the the old raid cluster?

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The OS should not be in the RAID configuration at all. Here's what you can do:

Option 1

Install your OS on a smaller partition of one of the drives, and partition the rest for use in the RAID cluster.

So, assuming you're using 4 disks:

  • Disk 1: 50GB for OS, 10GB for Swap, 1900GB for RAID partition
  • Disk 2-4: 1900GB partitions each.

Option 2

Keep OS on a separate disk.

So, assuming you're using 5 disks:

  • Disk 1: Contains OS. Not included in RAID cluster.
  • Disks 2-5: Partition however you want, say 2000GB each. These will make up the RAID cluster.

In either option 1 or 2, you should be able to reinstall the OS without destroying the RAID cluster.

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Why should the OS not be included with the RAID config? – KronoS Jan 31 '11 at 4:00
I don't really have a great answer for this. This has to do with ease of rebuilding the array if there happens to be a failure, or if you want to migrate the array. Another possibility might be to have the OS mirrored (using RAID 1) and use the rest of the disks for RAID 5. That way both your data and OS are protected against 1 disk failure, each. – aqua Jan 31 '11 at 7:11

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