View source for Mdraid

== Prepare the hard drives ==

In this example we create a RAID just for storage, so we only have one Partition on each drive.

{{Code|GPT partition layout for RAID|
<pre>
/dev/sdb	2.7 TiB	FD00	Linux RAID
/dev/sdc	2.7 TiB	FD00	Linux RAID
</pre>
}}

{{Root|gdisk /dev/sdb}}

We leave 100M of free space on the end of the device, just to be on the safe side if we have to replace a drive and won't be able to get an identical one which has the exact same amount of sectors.

{{Code|gdisk commands|
<pre>
Command (? for help): p
Disk /dev/sdb: 5860533168 sectors, 2.7 TiB
[...]

n
1
enter
-100M
fd00

p
w
Y
</pre>
}}


== Create the RAID array ==


=== RAID 1 ===

{{Root|<nowiki>mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1</nowiki>}}


=== RAID 5===

{{Root|<nowiki>mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sd[b-d]1</nowiki>}}


=== Checking the progress ===

{{Root|cat /proc/mdstat}}
{{Root|mdadm --detail /dev/md0}}

{{Note|Don't be scared when you see [UU_], initially the raid is created in a degraded state, when the process is completed it should show [UUU].}}

{{Root|mdadm --examine /dev/sdb1}}


== Create the file system ==

Useful for calculating the options: http://uclibc.org/~aldot/mkfs_stride.html


=== RAID 1===

Nothing special here besides specifying the block size to be sure it's using 4096.

{{Root|mkfs.ext4 -b 4096 /dev/md0}}


=== RAID 5===

* chunk size = 512KiB (mdadm --detail /dev/md0 | grep "Chunk Size")
* block size = 4KiB (recommended for large files, and most of time)
* stride = chunk / block here 512KiB / 4KiB = 128
* stripe-width = stride * ( (n disks in raid5) - 1 ) here: 128 * ( (3) - 1 ) = 256

{{Root|<nowiki>mkfs.ext4 -b 4096 -E stride=128,stripe-width=256 /dev/md0</nowiki>}}


== Label ==
{{Root|tune2fs -L raid /dev/md0}}


== Free space reserved for root ==
{{Warning|Don't do this to partitions containing a linux os, only to plain storage partitions.}}

{{Root|tune2fs -m 0 /dev/md0}}


== fstab ==

{{Root|blkid}}

{{Code|/etc/fstab|
<pre>
UUID=b036ad79-939f-d4ae-e2c0-2f3f5c2e7087	/mnt/raid	ext4	defaults,noatime	0 2
</pre>
}}


== Update /etc/mdadm.conf ==
{{Root|mdadm --detail --scan >> /etc/mdadm.conf}}

{{Code|/etc/mdadm.conf|
<pre>
ARRAY /dev/md0 metadata=1.2 name=host:0 UUID=b036ad79:939fd4ae:e2c02f3f:5c2e7087
MAILADDR admin@mail.local
</pre>
}}


== Mount ==
{{Root|mkdir -p /mnt/raid}}
{{Root|mount /mnt/raid}}


== Enable mdadm.service ==
{{Root|systemctl enable mdadm.service}}