I've got a RAID5 array comprised of 4 x 3TB drives which is 97% full and would like to grow the array by adding a 5th drive of the same make/ model. Looking at https://raid.wiki.kernel.org/index.php/Growing it seems the approach (after partitioning the drive) is to: 1) add the drive to the pool: # mdadm --add /dev/md127 /dev/sdX1 2) grow the array: # mdadm --grow --raid-devices=5 --backup-file=~/grow_md127.backup /dev/md127 3) edit mdadm.conf to include the 5th drive i.e. num-devices=5 4) determine raid stride size calculated with chunk / block 4) ensure the array is unmounted and resize ext4: # resize2fs -S ascertained_stride_size -p /dev/md127 Is the above correct, apart from making sure I have a good backup and do this via UPS power, are there any other considerations? I'm also wondering whether there's a faster way to achieve the addition/resync Looking at man mdadm it mentions: --assume-clean Tell mdadm that the array pre-existed and is known to be clean. It can be useful when trying to recover from a major failure as you can be sure that no data will be affected unless you actually write to the array. It can also be used when creating a RAID1 or RAID10 if you want to avoid the initial resync, however this practice — while normally safe — is not recommended. Use this only if you really know what you are doing. When the devices that will be part of a new array were filled with zeros before creation the operator knows the array is actually clean. If that is the case, such as after running badblocks, this argument can be used to tell mdadm the facts the opera‐ tor knows. When an array is resized to a larger size with --grow --size= the new space is normally resynced in that same way that the whole array is resynced at creation. From Linux version 3.0, --assume-clean can be used with that command to avoid the auto‐ matic resync. Does this mean that after partitioning the drive I can avoid the entire resync operation by calling: # mdadm --grow --assume-clean --raid-devices=5 --backup-file=~/grow_md127.backup /dev/md127 ? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
