Software RAID and LVM
|This article will provide an example of how to install and configure Parabola with a software RAID or Logical Volume Manager (LVM).|
|Installing with Fake RAID|
|Convert a single drive system to RAID|
- 1 Introduction
- 2 Installation
- 2.1 Load kernel modules
- 2.2 Prepare the hard drives
- 2.3 RAID installation
- 2.4 LVM installation
- 2.5 Update RAID configuration
- 2.6 Prepare hard drive
- 2.7 Configure system
- 2.8 Conclusion
- 2.9 Install Grub on the Alternate Boot Drives
- 2.10 Archive your Filesystem Partition Scheme
- 3 Management
- 4 Additional Resources
- 5 Acknowledgement
Although RAID and LVM may seem like analogous technologies they each present unique features. This article uses an example with three similar 1TB SATA hard drives. The article assumes that the drives are accessible as /dev/sda, /dev/sdb, and /dev/sdc. If you are using IDE drives, for maximum performance make sure that each drive is a master on its own separate channel.
|LVM Logical Volumes||/||/var||/swap||/home|
|LVM Volume Groups||/dev/VolGroupArray|
1.1 Swap space
Many tutorials treat the swap space differently, either by creating a separate RAID1 array or a LVM logical volume. Creating the swap space on a separate array is not intended to provide additional redundancy, but instead, to prevent a corrupt swap space from rendering the system inoperable, which is more likely to happen when the swap space is located on the same partition as the root directory.
1.2 MBR vs. GPT
The widespread Master Boot Record (MBR) partitioning scheme, dating from the early 1980s, imposed limitations which affected the use of modern hardware. GUID Partition Table (GPT) is a new standard for the layout of the partition table based on the UEFI specification derived from Intel. Although GPT provides a significant improvement over a MBR, it does require the additional step of creating an additional partition at the beginning of each disk for GRUB2 (see: GPT specific instructions).
1.3 Boot loader
This tutorial will use SYSLINUX instead of GRUB2. GRUB2 when used in conjunction with GPT requires an additional BIOS Boot Partition. Additionally, the 2011.08.19 Arch Linux installer does not support GRUB2.
GRUB2 supports the default style of metadata currently created by mdadm (i.e. 1.2) when combined with an initramfs, which has replaced in Arch Linux with mkinitcpio. SYSLINUX only supports version 1.0, and therefore requires the --metadata=1.0 option.
Some boot loaders (e.g. GRUB, LILO) will not support any 1.x metadata versions, and instead require the older version, 0.90. If you would like to use one of those boot loaders make sure to add the option --metadata=0.90 to the /boot array during RAID installation.
Obtain the latest installation media and boot the Parabola installer as outlined in the Beginners' Guide, or alternatively, in the Official Parabola Install Guide. Follow the directions outlined there until you have configured your network.
2.1 Load kernel modules
Enter another TTY terminal by typing raid0, raid1, raid5, raid6, raid10) and LVM (i.e. dm-mod) modules. The following example makes use of RAID1 and RAID5.+ . Load the appropriate RAID (e.g.
# modprobe raid1 # modprobe raid5 # modprobe dm-mod
2.2 Prepare the hard drives
Each hard drive will have a 100MB /boot partition, 2048MB /swap partition, and a / partition that takes up the remainder of the disk.
The boot partition must be RAID1, because GRUB does not have RAID drivers. Any other level will prevent your system from booting. Additionally, if there is a problem with one boot partition, the boot loader can boot normally from the other two partitions in the /boot array. Finally, the partition you boot from must not be striped (i.e. RAID5, RAID0).
2.2.1 Install gdisk
Update the pacman database:
Refresh the package list:
$ pacman -Syy
$ pacman -S gdisk
2.2.2 Partition hard drives
We will use
gdisk to create three partitions on each of the three hard drives (i.e. /dev/sda, /dev/sdb, /dev/sdc):
Name Flags Part Type FS Type [Label] Size (MB) ------------------------------------------------------------------------------- sda1 Boot Primary linux_raid_m 100.00 # /boot sda2 Primary linux_raid_m 2000.00 # /swap sda3 Primary linux_raid_m 97900.00 # /
Open gdisk with the first hard drive:
$ gdisk /dev/sda
and type the following commands at the prompt:
- Add a new partition:
- Select the default partition number:
- Use the default for the first sector:
- For sda1 and sda2 type the appropriate size in MB (i.e. +100MB and +2048M). For sda3 just hit to select the remainder of the disk.
- Select Linux RAID as the partition type: fd00
- Write the table to disk and exit:
Repeat this process for /dev/sdb and /dev/sdc or use the alternate sgdisk method below. You may need to reboot to allow the kernel to recognize the new tables.
2.2.3 Clone partitions with sgdisk
If you are using GPT, then you can use sgdisk to clone the partition table from /dev/sda to the other two hard drives:
$ sgdisk --backup=table /dev/sda $ sgdisk --load-backup=table /dev/sdb $ sgdisk --load-backup=table /dev/sdc
2.3 RAID installation
After creating the physical partitions, you are ready to setup the /boot, /swap, and / arrays with mdadm. It is an advanced tool for RAID management that will be used to create a /etc/mdadm.conf within the installation environment.
Create the / array at /dev/md0:
# mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sd[abc]3
Create the /swap array at /dev/md1:
# mdadm --create /dev/md1 --level=1 --raid-devices=3 /dev/sd[abc]2
Create the /boot array at /dev/md2:
# mdadm --create /dev/md2 --level=1 --raid-devices=3 --metadata=1.0 /dev/sd[abc]1
After you create a RAID volume, it will synchronize the contents of the physical partitions within the array. You can monitor the progress by refreshing the output of /proc/mdstat ten times per second with:
# watch -n .1 cat /proc/mdstat
Further information about the arrays is accessible with:
# mdadm --misc --detail /dev/md | less
Once synchronization is complete the State line should read clean. Each device in the table at the bottom of the output should read spare or active sync in the State column. active sync means each device is actively in the array.
2.4 LVM installation
This section will convert the two RAIDs into physical volumes (PVs). Then combine those PVs into a volume group (VG). The VG will then be divided into logical volumes (LVs) that will act like physical partitions (e.g. /, /var, /home). If you did not understand that make sure you read the LVM Introduction section.
2.4.1 Create physical volumes
Make the RAIDs accessible to LVM by converting them into physical volumes (PVs):
# pvcreate /dev/md0
Confirm that LVM has added the PVs with:
2.4.2 Create the volume group
Next step is to create a volume group (VG) on the PVs.
Create a volume group (VG) with the first PV:
# vgcreate VolGroupArray /dev/md0
Confirm that LVM has added the VG with:
2.4.3 Create logical volumes
Now we need to create logical volumes (LVs) on the VG, much like we would normally prepare a hard drive. In this example we will create separate /, /var, /swap, /home LVs. The LVs will be accessible as /dev/mapper/VolGroupArray-<lvname> or /dev/VolGroupArray/<lvname>.
Create a / LV:
# lvcreate -L 20G VolGroupArray -n lvroot
Create a /var LV:
# lvcreate -L 15G VolGroupArray -n lvvar
Create a /home LV that takes up the remainder of space in the VG:
# lvcreate -l +100%FREE VolGroupArray -n lvhome
Confirm that LVM has created the LVs with:
2.5 Update RAID configuration
Since the installer builds the initrd using /etc/mdadm.conf in the target system, you should update that file with your RAID configuration. The original file can simply be deleted because it contains comments on how to fill it correctly, and that is something mdadm can do automatically for you. So let us delete the original and have mdadm create you a new one with the current setup:
# mdadm --examine --scan > /etc/mdadm.conf
2.6 Prepare hard drive
Follow the directions outlined the Installation section until you reach the Prepare Hard Drive section. Skip the first two steps and navigate to the Manually Configure block devices, filesystems and mountpoints page. Remember to only configure the PVs (e.g. /dev/mapper/VolGroupArray-lvhome) and not the actual disks (e.g. /dev/sda1).
2.7 Configure system
- Add the dm_mod module to the MODULES list in /etc/mkinitcpio.conf.
- Add the mdadm_udev and lvm2 hooks to the HOOKS list in /etc/mkinitcpio.conf after udev.
Once it is complete you can safely reboot your machine:
2.9 Install Grub on the Alternate Boot Drives
Once you have successfully booted your new system for the first time, you will want to install Grub onto the other two disks (or on the other disk if you have only 2 HDDs) so that, in the event of disk failure, the system can be booted from another drive. Log in to your new system as root and do:
# grub grub> device (hd0) /dev/sdb grub> root (hd0,0) grub> setup (hd0) grub> device (hd0) /dev/sdc grub> root (hd0,0) grub> setup (hd0) grub> quit
2.10 Archive your Filesystem Partition Scheme
Now that you are done, it is worth taking a second to archive off the partition state of each of your drives. This guarantees that it will be trivially easy to replace/rebuild a disk in the event that one fails. You do this with the
sfdisk tool and the following steps:
# mkdir /etc/partitions # sfdisk --dump /dev/sda >/etc/partitions/disc0.partitions # sfdisk --dump /dev/sdb >/etc/partitions/disc1.partitions # sfdisk --dump /dev/sdc >/etc/partitions/disc2.partitions
4 Additional Resources
- Setup Arch Linux on top of raid, LVM2 and encrypted partitions by Yannick Loth
- RAID vs. LVM on Stack Overflow
- What is better LVM on RAID or RAID on LVM? on Server Fault
- Managing RAID and LVM with Linux (v0.5) by Gregory Gulik
- Gentoo Linux x86 with Software Raid and LVM2 Quick Install Guide
- 2011-09-08 - Arch Linux - LVM & RAID (1.2 metadata) + SYSLINUX
- 2011-04-20 - Arch Linux - Software RAID and LVM questions
- 2011-03-12 - Arch Linux - Some newbie questions about installation, LVM, grub, RAID