Mdraid Q On C6…

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so, I installed a c6 system offsite today, had to do it in a hurry.
box has 2 disks meant to be mirrored… I couldn’t figure out how to get anaconda to build a LVM root on a mirror, so I ended up just installing a /boot and vg_system on sda and raid it later.

every howto I find for linux says to half-raid the OTHER disk, COPY
everything to it, then boot from it and wipe the first disk and then bond it as a mirror of the 2nd. Thats kind of ugly.

in solaris, you can tell it that your existing partition is half of a mirror, update /etc/vfstab, then reboot, and then join a mirror to it.
this seems much cleaner to me than copying everything.

I tried to do this the solaris way, and at the first step, am told…

# mdadm –create /dev/md0 –level=mirror –raid-devices=2 /dev/sda2
missing
mdadm: cannot open /dev/sda2: Device or resource busy

/dev/sda2 contains the LVM root vg…

so… I’m thinking I”ll boot a rescue system from usb, create the half mirror, then reboot to the incomplete raid and add mirror /dev/sdb2

will the VG be found on /dev/md0 instead of on /dev/sda2 ?
if so, is there any other reason this won’t work?

6 thoughts on - Mdraid Q On C6…

  • this is a 32 bit old/small server. its doing audio processing for an internet radio station, so it really shouldn’t be a VM.

    and I haven’t seen any CentOS with a zfs / … this system has 2 240GB
    disks which are meant to be mirrored.

  • Why a VM?

    Its a bit fiddly to set up / but it works and is several orders of magnitude more awesome than LVM and ext/xfs.

  • If you create just a RAID1 then you can get away with 1 failed device. I
    do not think RAID10 will be accepted with just one device + one failed.

    There might be option to just change the type of partition on existing HDD and write metadata with mdraid command, joining it to some existing raid device, but I never tried it and I would not attempt it on important hdd’s.

    And here are commands for fast partition + RAID1 + RAID10 creation:

    https://www.facebook.com/notes/CentOS/creating-partitions-for-raid/10151764130747728

  • The installer’s graphical mode (as opposed to how it worked in EL5 with text mode) is the only interactive way to edit partitioning on EL6.

    In your kickstart file,
    – specify the partitioning
    – specify “graphical” keyword to boot to the graphical installer

    Makes sense to me. There’s metadata written to the mdadm underlying devices.

    What does Solaris magically do that allows this to be supported work?
    ( I’m not familiar with Solaris so I’d be curious to know. )

    if so, is there any other reason this won’t work?

    I believe if you do find away to get it to work, you’ll have major problems with the partition and not the raid getting mounted.

    And to comments about RAID10, it is not possible to add disks to a RAID10
    array. Although I’ve not done it (my RAID10s are in hardware) I’d expect you could specify missing disk members.

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