howto/raid.md

@@ -33,6 +33,70 @@ drive models.
 Note that Hetzner also has [pretty good documentation on how to deal
 with SMART output](https://wiki.hetzner.de/index.php/Seriennummern_von_Festplatten_und_Hinweise_zu_defekten_Festplatten/en).
 
+## Building a new array
+
+Assume our new drives are `/dev/sdc` and `/dev/sdd`, and the highest array we have is
+`md1`, so we're creating a new `md2` array:
+
+ 1. Partition the drive. Easiest is to reuse an existing drive, as
+    above:
+
+        sfdisk -d /dev/sda | sfdisk --no-reread /dev/sdc --force
+        sfdisk -d /dev/sda | sfdisk --no-reread /dev/sdd --force
+
+    Or, for a fresh new drive in a different configuration, partition
+    the whole drive by hand:
+
+        for disk in /dev/sde /dev/sdd ; do
+          parted -s $disk mklabel gpt &&
+          parted -s $disk -a optimal mkpart primary 0% 100%
+        done
+
+ 2. Create a RAID-1 array:
+
+        mdadm --create --verbose --level=1 --raid-devices=2 \
+               /dev/md2 \
+               /dev/sde1 /dev/sdd1
+
+    Create a RAID-10 array with 6 drives:
+
+         mdadm --create --verbose --level=10 --raid-devices=6 \
+               /dev/md2 \
+               /dev/sda1 \
+               /dev/sdb1 \
+               /dev/sdc1 \
+               /dev/sdd1 \
+               /dev/sde1 \
+               /dev/sdf1
+
+ 3. Setup full disk encryption:
+
+         cryptsetup luksFormat/dev/md2 &&
+         cryptsetup luksOpen /dev/md2 crypt_dev_md2 &&
+         echo crypt_dev_md2 UUID=$(lsblk -n -o UUID /dev/md2 | head -1) none luks,discard | tee -a /etc/crypttab &&
+         update-initramfs -u
+
+    With an on-disk secret key:
+
+         dd if=/dev/random bs=64 count=128 of=/etc/luks/crypt_dev_md2 &&
+         chmod 0 /etc/luks/crypt_dev_md2 &&
+         cryptsetup luksFormat --key-file=/etc/luks/crypt_dev_md2 /dev/md2 &&
+         cryptsetup luksOpen --key-file=/etc/luks/crypt_dev_md2 /dev/md2 crypt_dev_md2 &&
+         echo crypt_dev_md2 UUID=$(lsblk -n -o UUID /dev/md2 | head -1) /etc/luks/crypt_dev_md2 luks,discard | tee -a /etc/crypttab &&
+         update-initramfs -u
+
+From here, the array is ready for use in
+`/dev/mapper/crypt_dev_md2`. It will be resyncing for a while, you can
+see the status with:
+
+    watch -d cat /proc/mdstat
+
+You can either use it as is with:
+
+    mkfs -t ext4 -j /dev/mapper/crypt_dev_md2
+
+... or add it to LVM, see [LVM docs](howto/lvm).
+
 # Hardware RAID
 
 Note: we do not have hardware RAID servers, nor do we want any in the