Failed RAID 5 Rebuild and Recovery
Keep a comprehensive on-site maintenance log of all activities, who did what and on what date.
Make sure you record the physical order, location, time date of install and connection of all the system units especially the hard drives. Visibly label the hard drive units with their place order in the system along with date of install whilst the system is functioning correctly.
RAID 5 System Maintenance Knowledge
Get familiar with your manufacture specific documentation such that you are proficient in the replacement and substitution of any failed components specifically a single failed hard disk drive.
Ensure you have a fault reporting routine that will facilitate a response to a system fault immediately it is flagged, particularly a hard disk drive drop-out.
RAID 5 Maintenance.
Back-up your system and test the back-up capability by removing one of the drives from the subsystem while it’s running. Replace this drive with an exact match model and type blank hard drive, then allow the system to rebuild to un-degraded operational state (This may take a relatively long time)
Note that if two live hard drives fail simultaneously there is no possibility of a successful auto rebuild and a specialised data recovery service will be needed to restore your system to an operational state.
Be aware that a system rebuild using a corrupt volume will not repair the data integrity and will almost certainly cause further damage to the system operational data.
Things to know about RAID 5 Systems.
- RAID 5 is not a back-up solution, it is a performance option.
- RAID 5 with multiple hard drive fail need specialist attention, never attempt a rebuild that will potentially overwrite your data files.
- RAID 5 rebuilds require all drive members installed, never attempt a rebuild from a system that is not fully provisioned.
- In a RAID 5 system, stored data is written to a hard drives in sequence. Never swap out hard drives from other live locations within the array or shuffle them about.
- Never remove more than one hard disk drive at a time from a RAID 5 system.
- We advise never to run check disk type utilities on failed or failing RAID drives. They can cause mayhem when reallocating dud data areas.
The RAID 5 hot spare dilemma.
RAID 5 recovery and maintenance actions ought to be:
- Run a data backup.
- Check the back-up.
- Find the bad drive. i.e. check serial number is that reported by RAID controller.
- Replace the bad hard disk for a new, unused one.
- Start the rebuild of the RAID.
During a RAID 5 rebuild there is an increased probability of an additional drive failure, Using a Hot-Spare your RAID will skip the first two steps and a rebuild will be attempted before a contingency back-up is available Running a Hot-Spare is therefore not recommended for certain critical applications.
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