RAID away

During the last week I’ve replaced the disks of my software RAID with larger ones as the capacity was exceeded. While this is theoretically an easy task, I had to learn a few things along the way:

  • Trying to perform such an upgrade on a headless system without console will fail.
  • fdisk silently fails to parse integer values larger than 2147483647.
  • The md superblock is located at the end of the partition/disk that you add to the RAID.
  • If the kernel associates the complete drive to a specific md device instead of the last partition, blocking the use of other partitions for other md devices, resize the last partition to leave some (wasted) space at the end to ensure that the end of the last RAID partition differs from the end of the drive.
  • Some manufactures build ‘green’ disks that constantly unload/load their heads, causing the drive to run out of spec in a very short time. If the manufacturer provides a DOS tool to correct that behavior, a pretty easy solution is to put it onto a bootable CD.
  • This stride calculation script helps to optimize the performance of the¬†filesystem¬†running on a RAID5.
  • Cheap desktop drives might be a bad choice for a RAID, if they break during the first re-sync of the RAID you can try to recover your data by re-creating the RAID – Thanks, Adrian!

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