The RAID controller reports 'degraded', one disk has failed.
A single failed disk in RAID 1, 5, 6 or 10 means no data loss, but you are now vulnerable. Don't panic, do act fast and stick to a procedure.
Try this first
- 1Identify the bad disk: serial number and slot in iDRAC/iLO/IPMI or your RAID management tool. Do not rely on the LED, write it down.
- 2Ensure you have a hot spare or a replacement disk of exactly the same model and size (or newer/larger, but same type SAS/SATA and speed).
- 3Hot-swap the disk while the system runs if the chassis supports it. Otherwise plan downtime first.
- 4Monitor the rebuild: can take hours to a day on large NL-SAS drives. The array is extra vulnerable during rebuild, so do not yank a second disk.
- 5After rebuild: check SMART on the other disks, because when one dies the neighbours from the same batch often follow.
When to bring us in
RAID 5 with large drives (>4 TB) has a serious rebuild failure rate. Next refresh: RAID 6 or a separate RAID 10 with smaller disks. Always run a fresh backup test before the rebuild starts.
See also
- One DC or two DCs for an SMB office?Two is almost always the right answer; one DC is a single point of failure for logon, DNS and GPOs.
- Should I split FSMO roles across two DCs?For a small domain all on one DC is fine; with two DCs splitting is tidier but not required.
- How do I know my AD replication is healthy?Replication errors creep in silently; they only surface when logins or GPOs misbehave.
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