3 Replies Latest reply on Jun 19, 2013 4:54 PM by sylvia_intel

    RAID size



      I'm working on a script that should automatically provision servers. Server I'm working on are Supermicro X9DRW that have HDDs connected to the onboard RAID controller. One of the function of my script is to create RAID1 volume for the OS install. Creation is working fine, but I have noticed that volume created by my script is utilizing the whole space on the HDD, while volume created by the RSTe firmware is always 5% smaller than the size of the physical drives. Tried this with drives of different sizes and in each case 5% was not used.

      Is there any particular reason why the 5% of the drive is "reserved"? I've checked the "Intel Rapid Storage Technology enterprise for Linux OS" document, and could not find any answer to my question. Moreover, commands specified in section 5 "Volume creation" create volume that is utilizing the whole drive.

      Anyone seen that before?




        • 1. Re: RAID size

          Hello Pkilar,

          How are you running your script? Within the operating system or before loading it?

          Remember that the OS created a reserved disk space to write the metadata.


          • 2. Re: RAID size

            Hello Sylvia,

            I'm running the script before loading the OS - it is being executed from within Linux's initrd.

            Here is the actual script:


            mdadm --remove /dev/md126

            mdadm --remove /dev/md127

            mdadm --stop /dev/md126

            mdadm --stop /dev/md127

            mdadm --zero-superblock /dev/sd[a-b]

            sync && sync

            rm -f /dev/md/*

            dd if=/dev/zero conv=fsync of=/dev/sda bs=1M count=32

            dd if=/dev/zero conv=fsync of=/dev/sdb bs=1M count=32

            blockdev --rereadpt /dev/sda

            blockdev --rereadpt /dev/sdb

            export IMSM_NO_PLATFORM=1

            mdadm --create /dev/md/imsm --force --raid-devices=2 --spare-devices=0 --metadata=imsm --assume-clean /dev/sd[a-b]

            mdadm --create /dev/md/System --force --raid-devices=2 --spare-devices=0 --level=1 --assume-clean /dev/md/imsm


            As I have mentioned in my first post, the script works fine and it can create RAID that can utilize the whole capacity of the underlying drives. However, when I create RAID on the same server and the same drivers, but I use the "Intel SCU Option ROM" to create it, the size of the RAID volume is 5% smaller than the capacity of the drives. Please see below:

            Intel(R) Rapid Storage Technology enterprise - SCU Option ROM -
                      Copyright(C) 2003-12 Intel Corporation.  All Rights Reserved.

            **********************************[ MAIN MENU ]*********************************

            *         1.  Create RAID Volume             3.  Reset Disks to Non-RAID       *

            *         2.  Delete RAID Volume             4.  Exit                          *

            ***************************[ DISK/VOLUME INFORMATION ]**************************

            * RAID Volumes:                                                                *

            * ID   Name              Level             Strip      Size Status      Bootable*

            * 0    System            RAID1(Mirror)     N/A     884.9GB Normal        Yes   *

            *                                                                              *

            * Physical Devices:                                                            *

            * ID   Device Model     Serial #                     Size Type/Status(Vol ID)  *

            * 4    ST91000640NS     9XG2W6CW                  931.5GB Member Disk(0)       *

            * 5    ST91000640NS     9XG30KBR                  931.5GB Member Disk(0)       *

            *                                                                              *

            *                                                                              *

            *                                                                              *

            *                                                                              *


                      [**]-Select          [ESC]-Exit           [ENTER]-Select Menu


            What is this 5% used for? Is it necessary or recommended to create RAID volume slightly smaller than then physical drive, or is the volume created by the mdadm command without specifying the "--size" parameter correct.


            Thank you very much for your reply.



            • 3. Re: RAID size


              I was doing some research and it looks like this 5% is reserved on every RAID volume, even though the RAID controller is Intel or any other brand.


              This space could be reserved for important root processes or for any possible rescue actions.


              For more information you may want to search on Google typing “Reserved space for root”