In this lesson, you will learn how to build flexible storage hierarchies by using specific disk partitions as building blocks for software RAID arrays instead of entire physical disks.
Beyond Whole-Disk RAID
When we talk about software RAID using mdadm, the common tendency is to dedicate an entire physical drive (like /dev/sda) to an array. However, you aren't limited to this. By using partitions, you can carve a single physical drive into multiple segments and assign them to different RAID levels simultaneously.
This technique is essential for designing complex storage hierarchies. For example, if you have two 1TB drives, you could partition each into two 500GB segments. You can then use the first set of segments to create a RAID 1 (mirror) for your critical OS data, while using the second set of segments to form a RAID 0 (stripe) for high-speed scratch space.
Implementation Example
To create an array using partitions, you simply point mdadm at the device files for the partitions (e.g., /dev/sda1) rather than the raw drive.
# Assuming /dev/sda1 and /dev/sdb1 are prepared partitions
sudo mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
# You can simultaneously use other partitions on those same drives
sudo mdadm --create /dev/md1 --level=0 --raid-devices=2 /dev/sda2 /dev/sdb2
Why Stack RAID via Partitions?
Stacking RAID via partitions allows you to maximize hardware utility. It transforms a fixed physical drive into a multi-purpose storage resource. This is particularly useful in environments where you need to isolate workloads or manage specific capacity needs without buying additional hardware.
However, keep in mind that since the partitions share the same physical spindle or flash controller, your IO performance will be constrained by the drive's physical limitations. If the physical drive fails, both RAID arrays using its partitions will likely suffer data loss unless you have planned your parity and redundancy carefully across separate physical disks.
Key Takeaway: Partition-based RAID allows you to segment physical hardware into distinct RAID arrays, enabling multi-tiered storage layouts on a single set of disks.