RAID levels in practice: reading and recovering a degraded array (Linux md and Storage Spaces)
For system administrators and MSP technicians who already know the RAID levels and how to find a failing disk, and now have to act when an array reports 'degraded'. It builds on 'RAID concepts and limitations' and 'Handling disk failures'. You'll work out how many more failures an array can take once a member has gone, read the status output of Linux software RAID (mdadm, /proc/mdstat, sysfs) and Windows Storage Spaces, choose a safe replacement plan, follow a rebuild to a verified finish, and make sure the next degradation raises an alert. Hardware RAID controllers use the same ideas through their own tools; follow the vendor's procedure for those. Ends with a supervisor-graded failure-and-recovery exercise on a lab array.
- Level
- Intermediate
- Length
- About 105 minutes
- Contents
- 5 lessons · final exam
- Status
- Published · updated 10 Oct 2026
Skills you'll practise
- Calculate usable capacity and remaining failure tolerance for an array before and after a member fails
- Read a degraded array's status in Linux md (/proc/mdstat, mdadm --detail, sysfs) and in Storage Spaces
- Choose a safe response to a degraded array, including backup, disk identification and the replacement method
- Monitor a rebuild and confirm redundancy is restored, including a scrub check afterwards
- Set up alerting so a degraded array is noticed and tested, using mdadm monitor mode or a scripted health check
Course outline
- 1.Calculate usable capacity and remaining failure toleranceLesson · 18 min
- 2.Read a degraded array's status in Linux md and Storage SpacesLesson · 22 min
- 3.Choose a safe response to a degraded arrayLesson · 22 min
- 4.Monitor a rebuild and confirm redundancy is restoredLesson · 20 min
- 5.Set up alerting so a degraded array is noticedLesson · 15 min
- 6.RAID levels in practice: reading and recovering a degraded array (Linux md and Storage Spaces): knowledge checkKnowledge check · 14 questions
- 7.RAID levels in practice: reading and recovering a degraded array (Linux md and Storage Spaces): practical exerciseKnowledge check · 1 question
- 8.Final exam10 questions · passing it completes the course, so people who already know the material can test out
Sources it draws on
The lessons and questions are written from these references, so learners can go back to the original.
- mdadm(8): manage MD devices aka Linux Software RAID (Linux manual page)
- md(4): Multiple Device driver aka Linux Software RAID (Linux manual page)
- The Linux Kernel documentation: RAID arrays (md admin guide, sysfs attributes)
- Linux RAID Wiki (archived): Mdstat
- Linux RAID Wiki (archived): Replacing a failed drive
- Microsoft Learn: Storage Spaces and Storage Spaces Direct health and operational states
- Microsoft Learn: Storage Spaces overview (simple, mirror and parity resiliency)
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