Talk:Partitioning RAID / LVM on RAID

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I recently had to play musical extents on a massive LVM-on-RAID(s) volume and I wrote down the steps so I'd have them if I had to do it again. I think this wiki would be a good place to post these steps, but I'm not sure where in the wiki exactly to put it. Any thoughts? Gregory.dulin 14:04, 14 April 2010 (UTC)

  pvmove <PhysicalVolumePath>
  pvmove /dev/md2

moves Physical Extents (PE) off the Physical Volume (PV) you'll be rebuilding, and onto free PEs on other PVs in the VG.

  vgreduce <VolumeGroupName> <PhysicalVolumePath>
  vgreduce VolGroup00 /dev/md2

remove the PV from the VG

  pvremove <PhysicalVolumePath>
  pvremove /dev/md2

remove the PV from LVM entirely.

  cat /proc/mdstat > currentRAIDsetup.txt

make a note of which drives belong to which md devices (really useful if there are lots of md's)

  cat /proc/mdstat | grep <PhysicalVolume (no path)>
  cat /proc/mdstat | grep md2

make a note of the specific partitions we're working with

  mdadm --stop <PhysicalVolumePath>
  mdadm --stop /dev/md2

stop the RAID device

          • Repeated for each Disk *****
  fdisk -lu <DiskPath>
  fdisk -lu /dev/sdc

determine the start sector of the partition we want to align

determine the proper sector to start the partition on using this (excel) formula: =2048-(MOD(A1,2048))+A1 Put your current starting sector in cell A1 The output should be greater than the original start sector, and divisible by 2048

  cat /proc/mdstat | grep <PartitionPath w/o /dev/>
  cat /proc/mdstat | grep sdc2

make damn sure we're not going to be messing with anything live NOTE: Do NOT use /dev/ in front of your partition in this line (This command should NOT give you any output. If it does, then the partition you're about to fiddle with is still in use and bad things will happen.)

  parted <DiskPath>
  parted /dev/sdc

I don't like fdisk

  unit s

Change units to sectors


Note the partition number and the End Sector for the partition we're fiddling with

  rm <partition number>
  rm 2

deletes the partition

  mkpart <partition type> <aligned start sector>s <original end sector>s
  mkpart primary 2109440s 976768064s

create a new partition with the beginning aligned along a 1MiB (2048 sector) boundary (end alignment doesn't matter as far as I can figure). DON'T FORGET THE "s" !!!

  set <partition number> raid on
  set 2 raid on

sets the RAID flag to ON. Not necessary, but it doesn't hurt.


exits the parted program

          • End of Repeated for each Disk *****
  cat currentRAIDsetup.txt

so you can see what partitions to reassemble

  mdadm --create <PhysicalVolumePath> --level=<desired RAID level> --raid-devices=<number of drives> <device 1> <device 2> <device n...>
  mdadm --create /dev/md8 --level=5 --raid-devices=6 /dev/sdj2 /dev/sdr2 /dev/sdz2 /dev/sdah2 /dev/sdap2 /dev/sdb2

recreate the array with the newly aligned partitions

  gedit /etc/mdadm.conf

comment (#) out the line referring to your newly aligned md device (the UUID will be wrong) save the file and kill gedit

  mdadm --detail --scan | grep <PhysicalVolumePath> >> /etc/mdadm.conf
  mdadm --detail --scan | grep /dev/md8 >> /etc/mdadm.conf

write the configuration for your new md device to mdadm.conf so it gets reassembled on boot

  pvcreate <PhysicalVolumePath> --dataalignment 1024k
  pvcreate /dev/md8 --dataalignment 1024k

make the new volume an LVM Physical Volume

  vgextend <VolumeGroupName> <PhysicalVolumePath>
  vgextend VolGroup00 /dev/md8

Adds the newly aligned volume back into the VG

Repeat as necessary Gregory.dulin 14:04, 14 April 2010 (UTC)

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