Raid1 with LVM from scratch

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In this manual, a RAID 1 volume will be created with LVM. In this tutorial, disk are mounted in system as /dev/sdX and /dev/sdY

Prerequisites

Software

Make sure to enable the lvm USE flag for sys-fs/lvm2:

FILE /etc/portage/package.use
# Enable support for the LVM daemon and related tools
sys-fs/lvm2 lvm

Install the LVM package:

root #emerge sys-fs/lvm2

Install GNU parted:

(parted)emerge sys-block/parted

Disk partitions create

Warning
Data on /dev/sdX and /dev/sdY will be lost. Be careful with disk names!

Create partitions on both disks with parted.

Start parted for /dev/sdX disk

root #parted -a optimal /dev/sdX

Set units to mib:

(parted)unit mib

Create GPT table on disk:

(parted)mklabel gpt

Create primary partition, use all available space:

(parted)mkpart primary 1 -1

Set partition name to raiddata0:

(parted)name 1 raiddata0

Add lvm flag to new partition:

(parted)set 1 lvm on

Result should be:

(parted)print
Model: ATA ST6000VN0033-2EE (scsi)
Disk /dev/sdc: 6001GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name       Flags
 1      1049kB  6001GB  6001GB               raiddata0  lvm

Execute same parted commands for /dev/sdY.

LVM

Next steps will be to create physical volumes on both disks, add both physical volumes to a volume group, and create a logical volume with RAID 1 logic.

Physical volume

Create physical LVM volumes on the first disk's first partition:

root #lvm pvcreate /dev/sdX1

Create physical LVM volumes on the second disk's first partition:

root #lvm pvcreate /dev/sdY1

Volume group

Include both physical volumes to one volume group with name raid0vg0:

root #vgcreate raid0vg0 /dev/sdX1 /dev/sdY1

Now both disks are in the same volume group.

Logical Volume

Create logical volume with name raid0lv0 on volume group raid0vg0 with RAID 1 logic, using all available space. --nosync means skip the initial synchronization for RAID 1 (because this is a new RAID without any data on it):

root #lvcreate --mirrors 1 --type raid1 -l 100%FREE --nosync -n raid0lv0 raid0vg0

Now RAID 1 is created on both disks /dev/sdX and /dev/sdY.

The final step is to create the filesystem and mount it on boot. See sections below.

Ext4 Filesystem (non encrypted)

Create filesystem on the logical volume raid0lv0 on volume group raid0vg0:

root #mkfs.ext4 /dev/raid0vg0/raid0lv0
Important
Do not forget to add lvm2 service at boot: rc-update add lvm2 boot
Important
Your kernel should include LVM modules in initrd or compiled into kernel.

Mount filesystem on boot

Run blkid to find UUID of the ext4 filesystem on raid0lv0:

root #blkid
...
/dev/mapper/raid0vg0-raid0lv0_rimage_0: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0_rimage_1: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
...

"10092fa9-43f5-421e-a0a1-ca96323c6388" is UUID of the ext4 filesystem on RAID 1.

Create mountpoint /mnt/data:

root #mkdir /mnt/data

Add an entry to /etc/fstab:

FILE /etc/fstab
...
UUID=10092fa9-43f5-421e-a0a1-ca96323c6388  /mnt/data        ext4        defaults        0 2
...

Ext4 Filesystem (encrypted with LUKS)

Important
Please, see Full Disk Encryption From Scratch Simplified — a guide which covers the process of configuring a drive to be encrypted using LUKS and btrfs.

Create LUKS AES encrypted partition on top of logical volume raid0lv0 in volume group raid0vg0 (RAID 1):

root #cryptsetup luksFormat -c aes-xts-plain64:sha256 -s 256 /dev/raid0vg0/raid0lv0

Map encrypted LUKS partition as raid0lv0encripted:

root #cryptsetup luksOpen /dev/raid0vg0/raid0lv0 raid0lv0encripted

Create ext4 filesystem on LUKS partition:

root #mkfs.ext4 /dev/mapped/raid0lv0encripted

Mount LUKS encrypted device on boot from LVM RAID 1

First, create directrory, that will contain keys for encrypting/decryption devices:

root #mkdir /etc/keyfiles
root #chmod 0400 /etc/keyfiles

Create 4k keyfile with name main:

root #dd if=/dev/urandom of=/etc/keyfiles/main bs=1024 count=4
root #chmod 0400 /etc/keyfiles/main

Add main keyfile to list of keys that can decrypt the disk (technically: add keyfile to LUKS slot)

root #cryptsetup luksAddKey /dev/raid0vg0/raid0lv0 /etc/keyfiles/main

Find UUID of LUKS device (should be same as logical volume raid0lv0)

root #blkid
/dev/sdc1: UUID="OxJaqA-yMAP-sOjE-T5BR-H9Lp-rtPN-pl7rFC" TYPE="LVM2_member" PARTLABEL="raiddata1" PARTUUID="9c794e91-22a8-4b58-bedd-c3f656d82bd9"
/dev/sdb1: UUID="gNcHvg-Rocv-pFFc-VzvF-49tX-D1d3-odSe2h" TYPE="LVM2_member" PARTLABEL="raiddata0" PARTUUID="70121885-4a45-4a2b-8d3e-49edd8fffd34"
/dev/mapper/raid0vg0-raid0lv0_rimage_0: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0_rimage_1: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0: UUID="cd5740a1-b642-4359-a0b9-af84a8f01092" TYPE="crypto_LUKS"
/dev/mapper/raid0lv0encripted: UUID="fc7ec587-35e4-4726-815d-e1693cd89b70" TYPE="ext4"

In this case it is UUID="cd5740a1-b642-4359-a0b9-af84a8f01092"

Add to file /etc/conf.d/dmcrypt

FILE /etc/conf.d/dmcrypt
target='raid0lv0encripted'
source=UUID='cd5740a1-b642-4359-a0b9-af84a8f01092'
key='/etc/keyfiles/main'

Add dmcrypt to be started at boot:

root #rc-update add dmcrypt boot

Create mountpoint /mnt/data:

root #mkdir /mnt/data

Find EXT4 filesystem UUID

root #blkid
/dev/sdc1: UUID="OxJaqA-yMAP-sOjE-T5BR-H9Lp-rtPN-pl7rFC" TYPE="LVM2_member" PARTLABEL="raiddata1" PARTUUID="9c794e91-22a8-4b58-bedd-c3f656d82bd9"
/dev/sdb1: UUID="gNcHvg-Rocv-pFFc-VzvF-49tX-D1d3-odSe2h" TYPE="LVM2_member" PARTLABEL="raiddata0" PARTUUID="70121885-4a45-4a2b-8d3e-49edd8fffd34"
/dev/mapper/raid0vg0-raid0lv0_rimage_0: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0_rimage_1: UUID="10092fa9-43f5-421e-a0a1-ca96323c6388" TYPE="ext4"
/dev/mapper/raid0vg0-raid0lv0: UUID="cd5740a1-b642-4359-a0b9-af84a8f01092" TYPE="crypto_LUKS"
/dev/mapper/raid0lv0encripted: UUID="fc7ec587-35e4-4726-815d-e1693cd89b70" TYPE="ext4"

In our case it is UUID="fc7ec587-35e4-4726-815d-e1693cd89b70"

Add an entry to /etc/fstab:

FILE /etc/fstab
...
UUID=fc7ec587-35e4-4726-815d-e1693cd89b70  /mnt/data        ext4        defaults        0 2
...

Check LVM RAID 1 status

To check LVM RAID status for volume group raid0vg0:

root #lvs -a -o name,copy_percent,devices raid0vg0
  LV                  Cpy%Sync Devices                                  
  raid0lv0            100.00   raid0lv0_rimage_0(0),raid0lv0_rimage_1(0)
  [raid0lv0_rimage_0]          /dev/sdc1(1)                             
  [raid0lv0_rimage_1]          /dev/sdb1(1)                             
  [raid0lv0_rmeta_0]           /dev/sdc1(0)                             
  [raid0lv0_rmeta_1]           /dev/sdb1(0)

Performance tunnig

By default, in RAID 1, all disk are used for reading and writing. If one of disks is much slower then the other, it possible to improve write performance (with a small penalty to read performance) by disabling reading from the slowest drive.

In such scenario, the slowest drive will only write data (without reading), while the faster drive will read/write data.

root #lvchange --raidwritemostly /dev/sdb1 raid0vg0
Logical volume raid0vg0/raid0lv0 changed.

Where /dev/sdb1 is the physical volume in vg0 (slowest drive) and raid0vg0 is the volume group.

See also

  • LVM — allows administrators to create meta devices that provide an abstraction layer between a file system and the physical storage that is used underneath.
  • Full Disk Encryption From Scratch Simplified — a guide which covers the process of configuring a drive to be encrypted using LUKS and btrfs.

External resources

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