What happens when a disk in my RAID 4 or 5 volume stops working?

Good news — if one disk in your RAID 4 or RAID 5 volume fails, your data is safe and your volume will continue to work normally.

Why your data is protected

RAID 4 and RAID 5 volumes are designed with redundancy built in. As data is written to the volume, SoftRAID calculates “parity” information — a mathematical representation of your data — and stores it across the disks in your array. If any single disk fails completely, SoftRAID can use the parity data stored on the remaining disks to reconstruct everything that was on the failed drive, on the fly.

This means you can keep working normally while the failed disk is replaced. Your files remain fully accessible throughout.

What to do when a disk fails

Once you have replaced the failed disk with a new one, SoftRAID will automatically begin rebuilding the volume, restoring full redundancy. Until the rebuild is complete, your volume is operating without its safety net — so we recommend immediately updating all backups, and replacing the failed disk as soon as possible and avoiding any unnecessary risk to the remaining disks during this time.

Important: RAID 4 and RAID 5 can only survive the failure of one disk at a time. If a second disk fails before the rebuild is complete, data loss will occur.

For more information on how parity data is calculated and stored in RAID 4 and RAID 5 volumes, see our FAQ: RAID Levels.