Take a crash course in Ubuntu server administration and learn specific details that set Ubuntu Server apart from other platforms in this chapter from The Official Ubuntu Book.
If you look below the two physical drives that you used to have there, you'll notice a brand new drive, the Software RAID device that has one partition below it. That's your future /home partition, sitting happily on a RAID array. If you arrow over to it and hit Enter, you can now configure it just as you would a real partition.
The process is the same for any other partitions you want to toss into RAID. Create identical-sized partitions on all participating physical drives, select to use them as RAID space, enter the multidisk configurator (software RAID), and finally, create an array that uses the real partitions. Then create a filesystem on the newly created array.
Array Failure and Spare Devices
When a physical drive fails in a RAID array that's running in a level that provides redundancy—such as 1 or 5—the array goes into so-called degraded mode (never verbally abuse or be cruel to your RAID arrays!). Depending on the number of devices in the array, running in degraded mode might just have performance downsides, but it might also mean that another physical drive failure will bring down the whole array and cause total data loss. To recover the array from degraded mode, you need to add a working physical drive to the system (the old one can be removed) and instruct the array to use the new device to "rebuild."
In order to minimize the amount of time an array spends in degraded mode, and to prevent having to power off the machine to insert new physical drives if the server doesn't support hot-swapping, you can put extra physical drives into the machine and flag them as hot spares, which means the system will keep them active but unused until there's a drive failure. Cold spares, as the name implies, are just extra drives that you keep around on a shelf until there's a failure, at which point you manually add them to the array.
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