Last week we looked at making a single-disk system redundant by setting up a raid array. Today we’re going to see how to add a new disk to the array. It’s a good practice to have at least 3 disks, so in case one fails, you don’t have to worry about a devastating failure while a replacement is shipping.
Adding a disk is fairly easy using mdadm. You can follow these steps:
1. Install the drive into your machine
2. Boot and check fdisk -l to find its drive letter, in this example we’ll use /dev/sdg.
3. Partition the new drive using parted (commands you type are in bold):
parted -a optimal /dev/sdc GNU Parted 2.3 Using /dev/sdc Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) mklabel gpt Warning: The existing disk label on /dev/sdc will be destroyed and all data on this disk will be lost. Do you want to continue? Yes/No? yes (parted) mkpart primary 1 -1 (parted) align-check alignment type(min/opt) [optimal]/minimal? optimal Partition number? 1 1 aligned (parted) quit Information: You may need to update /etc/fstab.
4. Next add the partitioned drive to the array with madm:
mdadm --manage /dev/md0 --add /dev/sdc1
5. You’ll see it as a spare, this means it’s not being used:
/sbin/mdadm --detail /dev/md0 /dev/md0: Version : 1.2 Creation Time : Fri Feb 7 11:35:08 2014 Raid Level : raid1 Array Size : 471741248 (449.89 GiB 483.06 GB) Used Dev Size : 471741248 (449.89 GiB 483.06 GB) Raid Devices : 2 Total Devices : 3 Persistence : Superblock is persistent
Update Time : Thu Feb 13 09:18:17 2014 State : clean Active Devices : 2 Working Devices : 3 Failed Devices : 0 Spare Devices : 1
Name : devserver:0 (local to host devserver) UUID : a55fd0fe:7b142a4c:ad0d9a93:e97e9483 Events : 11194
Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 2 8 33 1 active sync /dev/sdb1
3 8 17 - spare /dev/sdc1
6. Lastly sync it by growing your RAID array:
mdadm --grow /dev/md0 --raid-devices=3
It’ll take a while to sync up before you see it as active sync in mdadm –detail /dev/md0. You can follow these same steps for each drive you add. You now have a three (or more!) drive redundant RAID1 array.