I have MFSYS25v2 systems in the field with 4 disks in an OS drive pool. The virtual drives for the OSs are set as RAID 10. I recently had a multiple disk failure on one of my systems that brought down the entire OS drive pool. Drives 1 and 3 failed. Normally in Raid 10 the RAID is written like this:
In RAID 10 data is striped across 1 and 3, 1 is mirrored to 2 and 3 is mirrored to 4. If drives 1 and 3 fail drives 2 and 4 have all of the required data to keep the array running.
This wasn't the case in my situation. As soon as drive 1&3 failed, all virtual drives were destroyed. It appears that RAID 10 on the Modular Server RAID controller is actually RAID 0+1. RAID 0+1 looks like this:
Notice that data is striped from Drive 1 to Drive 2. Drive 1 is mirrored to drive 3 and Drive 2 is mirrored to Drive 4. In my situation since Drive 1 and 3 failed all of my virtual drives failed. In RAID 0+1 you lose everything if drive 1&3 or drive 2&4 fail. This is not the case in RAID 10.
I am concerned that since RAID 0+1 is in use instead of RAID 10 the fault tolerance is negatively affected.
In this table it shows the RAID 10 can remain online in twice the number of scenarios as RAID 0+1. I would like clarification on this as it pertains to the Modular Server RAID controller.
Thanks,
Shane Linde