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Adding A New Disk To A Raid part 1

I have a RAID 5 array for all my data files. Recently I bought a new 3TB Hitachi hard drive and that was December 2016. I've been delaying using it until now. I've got some idle time today and tomorrow so it's perfect for hours and hours of syncing.

I've got new SATA data cables (the red ones) and the old power cables are still excellent. Used a philip screwdriver to fix the internal disks and tray. Turned on the computer.

[donato@archdesktop ~]$ ls -l /dev/ | grep sd
brw-rw----  1 root   disk    8,   0 Oct  6 17:46 sda
brw-rw----  1 root   disk    8,   1 Oct  6 17:48 sda1
brw-rw----  1 root   disk    8,  16 Oct  6 17:01 sdb
brw-rw----  1 root   disk    8,  17 Oct  6 17:01 sdb1
brw-rw----  1 root   disk    8,  18 Oct  6 17:01 sdb2
brw-rw----  1 root   disk    8,  32 Oct  6 17:01 sdc
brw-rw----  1 root   disk    8,  33 Oct  6 17:01 sdc1
brw-rw----  1 root   disk    8,  48 Oct  6 17:01 sdd
brw-rw----  1 root   disk    8,  49 Oct  6 17:01 sdd1
brw-rw----  1 root   disk    8,  64 Oct  6 17:01 sde

I want to see a list of all my devices and partitions to get the layout of my disks.

$sudo fdisk /dev/sda
Use fdisk to create a gpt table and create a partition.

$sudo fdisk -l /dev/sda
Disk /dev/sda: 2.7 TiB, 3000592982016 bytes, 5860533168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: F5255901-3E0B-47FE-A5CC-1FA421D88215

Device     Start        End    Sectors  Size Type
/dev/sda1   2048 5860533134 5860531087  2.7T Linux RAID

To add this device to my existing RAID, I used mdadm tool.

$man mdadm

$sudo mdadm --detail /dev/md127
##This is to get information on the current RAID array

This is a new disk but just to be sure you should check for any existing RAID info on the disk you are adding.
$sudo mdadm --examine /dev/sda1
##This is to check if the disk is clean or if it has been used in a RAID array before.

$sudo mdadm --manage /dev/md127 --add /dev/sda1
##This is to add the new disk to the RAID array. You should check the status of the array.
$sudo mdadm --detail /dev/md127

This is a RAID 5 array with pre-existing disk of 3 which is the required for level 5. The fourth disk would be added as a spare. You can stop here and my spare would be added automatically if one of the disks fail. But what if I want to activate and use the new disk right away?

Then I would have to modify the array. Specifically, I would have to grow the array.

$sudo mdadm --grow --raid-device=4 /dev/md127
##The RAID array will automatically start to sync the data over all the component devices and calculate parity and then write the data.

In my case, I have a total storage of 2TB x 2, 3TB x1, 1TB x1. mdadm has calculated that it will take just short of 6 hours to sync my data. Don't worry you can use the computer while mdadm finish up the sync. Just don't turn the computer off.

After the sync: what do I do after the sync?


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