4 Replies Latest reply on Mar 19, 2013 3:20 PM by Shane Linde

    Modular Server MFSYS25v2 RAID 10 appears to be 0+1

    Shane Linde

      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:

       

      raid10.JPG

      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:

       

       

      raid0+1.JPG

       

      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.

       

       

      raid comparison.JPG

      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

        • 1. Re: Modular Server MFSYS25v2 RAID 10 appears to be 0+1
          Dan_O

          The Modular Server does use RAID 0+1 for RAID 10.  I think the help file even says:

           

          RAID level 10

          In RAID level 10 (or 0+1), the RAID levels are "nested."

          • 2. Re: Modular Server MFSYS25v2 RAID 10 appears to be 0+1
            Shane Linde

            Thanks for the reply.  According to the RAID table I posted it looks like RAID 0+1 is a lot more vulnerable than RAID 10.  However,  I have had drives 2&3 fail in a 4 disk RAID 10 on a modular server and the Array was OK.  I would expect that 1&4 could possibly fail as well.  It would be nice if I could get something official from Intel that would identify which two drives could fail without the Array going down.

             

             

            Thanks,

             

            Shane

            • 3. Re: Modular Server MFSYS25v2 RAID 10 appears to be 0+1
              Dan_O

              On RAID 0+1, you can lose drives 1 and 4, or 2 and 3.

              On RAID 1+0, you can lose drives 1 and 2, or 3 and 4.

               

              Is that your understanding as well?

              • 4. Re: Modular Server MFSYS25v2 RAID 10 appears to be 0+1
                Shane Linde

                I have had drives 2&3 fail on a Modular Server RAID 10  (technically 0+1) with 4 drives and the array did not go down.

                 

                So I believe the following to be true:


                RAID 0+1 (What the modular server calls RAID10)

                 

                You can lose...

                1&2
                2&3
                3&4

                 

                I am unsure of 1&4 but would lean towards expecting it to stay online as you have the Original Disk 2 and the Mirror of Disk 1 albeit they are backwards in the array.

                 

                RAID 10

                You can lose...

                1&3

                2&4

                 

                1&4 - Like 0+1 you still have the original Disk 2 and the Mirror of Disk 1 just in a different order.

                 

                 

                So it actually looks like the RAID 0+1 that the Modular Server is calling RAID10 may be more resilient than the common RAID10 as it may be able to absorb 4 combinations of two drives failing vs. 3.