https://wiki.archlinux.org/api.php?action=feedcontributions&user=Drag0nius&feedformat=atomArchWiki - User contributions [en]2024-03-29T08:08:25ZUser contributionsMediaWiki 1.41.0https://wiki.archlinux.org/index.php?title=LVM_on_software_RAID&diff=254702LVM on software RAID2013-04-20T14:09:55Z<p>Drag0nius: /* Syslinux */</p>
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<div>[[ru:Installing with Software RAID or LVM]]<br />
[[Category:Getting and installing Arch]]<br />
[[Category:File systems]]<br />
{{Article summary start}}<br />
{{Article summary text|This article will provide an example of how to install and configure Arch Linux with a software RAID or Logical Volume Manager (LVM).}}<br />
{{Article summary heading|Required software}}<br />
{{Article summary link|Software|}}<br />
{{Article summary heading|Related}}<br />
{{Article summary wiki|RAID}}<br />
{{Article summary wiki|LVM}}<br />
{{Article summary wiki|Installing with Fake RAID}}<br />
{{Article summary wiki|Convert a single drive system to RAID}}<br />
{{Article summary end}}<br />
<br />
The combination of [[RAID]] and [[LVM]] provides numerous features with few caveats compared to just using RAID.<br />
<br />
== Introduction ==<br />
{{warning|Be sure to review the [[RAID]] article and be aware of all applicable warnings, particularly if you select RAID5.}}<br />
<br />
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 {{ic|/dev/sda}}, {{ic|/dev/sdb}}, and {{ic|/dev/sdc}}. If you are using IDE drives, for maximum performance make sure that each drive is a master on its own separate channel.<br />
<br />
{{tip|It is good practice to ensure that only the drives involved in the installation are attached while performing the installation.}}<br />
<br />
{| border="1" width="100%" style="text-align:center;"<br />
|width="150px" align="left" | '''LVM Logical Volumes'''<br />
|{{ic|/}}<br />
|{{ic|/var}}<br />
|{{ic|/swap}}<br />
|{{ic|/home}}<br />
|}<br />
{| border="1" width="100%" style="text-align:center;"<br />
|width="150px" align="left" | '''LVM Volume Groups'''<br />
|{{ic|/dev/VolGroupArray}}<br />
|}<br />
{| border="1" width="100%" style="text-align:center;"<br />
|width="150px" align="left" | '''RAID Arrays'''<br />
|{{ic|/dev/md0}}<br />
|{{ic|/dev/md1}}<br />
|}<br />
{| border="1" width="100%" style="text-align:center;"<br />
|width="150px" align="left" | '''Physical Partitions'''<br />
|{{ic|/dev/sda1}}<br />
|{{ic|/dev/sdb1}}<br />
|{{ic|/dev/sdc1}}<br />
|{{ic|/dev/sda2}}<br />
|{{ic|/dev/sdb2}}<br />
|{{ic|/dev/sdc2}}<br />
|}<br />
{| border="1" width="100%" style="text-align:center;"<br />
|width="150px" align="left" | '''Hard Drives'''<br />
|{{ic|/dev/sda}}<br />
|{{ic|/dev/sdb}}<br />
|{{ic|/dev/sdc}}<br />
|}<br />
<br />
=== Swap space ===<br />
{{note|If you want extra performance, just let the kernel use distinct swap partitions as it does striping by default.}}<br />
<br />
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.<br />
<br />
=== MBR vs. GPT ===<br />
{{Wikipedia|GUID Partition Table}}<br />
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 [[Wikipedia:Unified Extensible Firmware Interface|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: [[GRUB2#GPT specific instructions|GPT specific instructions]]).<br />
<br />
=== Boot loader ===<br />
This tutorial will use [[Syslinux|SYSLINUX]] instead of [[GRUB2]]. GRUB2 when used in conjunction with [[GUID Partition Table|GPT]] requires an additional [[GRUB2#GPT specific instructions|BIOS Boot Partition]]. Additionally, the [[DeveloperWiki:2011.08.19|2011.08.19]] Arch Linux installer does not support GRUB2.<br />
<br />
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 {{ic|<nowiki>--metadata=1.0</nowiki>}} option.<br />
<br />
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 {{ic|<nowiki>--metadata=0.90</nowiki>}} to the {{ic|/boot}} array during [[#RAID installation|RAID installation]].<br />
<br />
== Installation ==<br />
Obtain the latest installation media and boot the Arch Linux installer as outlined in the [[Beginners' Guide#Preparation|Beginners' Guide]], or alternatively, in the [[Official Arch Linux Install Guide#Pre-Installation|Official Arch Linux Install Guide]]. Follow the directions outlined there until you have [[Beginners Guide#Configure Network (netinstall)|configured your network]].<br />
<br />
==== Load kernel modules ====<br />
Enter another TTY terminal by typing {{Keypress|Alt}}+{{Keypress|F2}}. Load the appropriate RAID (e.g. {{ic|raid0}}, {{ic|raid1}}, {{ic|raid5}}, {{ic|raid6}}, {{ic|raid10}}) and LVM (i.e. {{ic|dm-mod}}) modules. The following example makes use of RAID1 and RAID5.<br />
# modprobe raid1<br />
# modprobe raid5<br />
# modprobe dm-mod<br />
<br />
=== Prepare the hard drives ===<br />
{{note|If your hard drives are already prepared and all you want to do is activate RAID and LVM jump to [[Installing_with_Software_RAID_or_LVM#Activate_existing_RAID_devices_and_LVM_volumes|Activate existing RAID devices and LVM volumes]]. This can be achieved with alternative partitioning software (see: [http://yannickloth.be/blog/2010/08/01/installing-archlinux-with-software-raid1-encrypted-filesystem-and-lvm2/ Article]).}}<br />
<br />
Each hard drive will have a 100MB {{ic|/boot}} partition, 2048MB {{ic|/swap}} partition, and a {{ic|/}} partition that takes up the remainder of the disk.<br />
<br />
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 {{ic|/boot}} array. Finally, the partition you boot from must not be striped (i.e. RAID5, RAID0).<br />
<br />
==== Install gdisk ====<br />
Since most disk partitioning software does not support GPT (i.e. {{Pkg|fdisk}}, {{Pkg|sfdisk}}) you will need to install {{Pkg|gptfdisk}} to set the partition type of the boot loader partitions.<br />
<br />
Update the [[pacman]] database:<br />
$ pacman-db-upgrade<br />
<br />
Refresh the package list:<br />
$ pacman -Syy<br />
<br />
Install {{Pkg|gptfdisk}}:<br />
$ pacman -S gdisk<br />
<br />
==== Partition hard drives ====<br />
We will use <code>gdisk</code> to create three partitions on each of the three hard drives (i.e. {{ic|/dev/sda}}, {{ic|/dev/sdb}}, {{ic|/dev/sdc}}):<br />
<br />
Name Flags Part Type FS Type [Label] Size (MB)<br />
-------------------------------------------------------------------------------<br />
sda1 Boot Primary linux_raid_m 100.00 # /boot<br />
sda2 Primary linux_raid_m 2000.00 # /swap<br />
sda3 Primary linux_raid_m 97900.00 # /<br />
<br />
Open {{ic|gdisk}} with the first hard drive:<br />
$ gdisk /dev/sda<br />
<br />
and type the following commands at the prompt:<br />
# Add a new partition: {{Keypress|n}}<br />
# Select the default partition number: {{Keypress|Enter}}<br />
# Use the default for the first sector: {{Keypress|Enter}}<br />
# For {{ic|sda1}} and {{ic|sda2}} type the appropriate size in MB (i.e. {{ic|+100MB}} and {{ic|+2048M}}). For {{ic|sda3}} just hit {{Keypress|Enter}} to select the remainder of the disk.<br />
# Select {{ic|Linux RAID}} as the partition type: {{ic|fd00}}<br />
# Write the table to disk and exit: {{Keypress|w}}<br />
<br />
Repeat this process for {{ic|/dev/sdb}} and {{ic|/dev/sdc}} or use the alternate {{ic|sgdisk}} method below. You may need to reboot to allow the kernel to recognize the new tables.<br />
<br />
{{note|Make sure to create the same exact partitions on each disk. If a group of partitions of different sizes are assembled to create a RAID partition, it will work, but ''the redundant partition will be in multiples of the size of the smallest partition'', leaving the unallocated space to waste.}}<br />
<br />
==== Clone partitions with sgdisk ====<br />
If you are using GPT, then you can use {{ic|sgdisk}} to clone the partition table from {{ic|/dev/sda}} to the other two hard drives:<br />
$ sgdisk --backup=table /dev/sda<br />
$ sgdisk --load-backup=table /dev/sdb<br />
$ sgdisk --load-backup=table /dev/sdc<br />
<br />
=== RAID installation ===<br />
After creating the physical partitions, you are ready to setup the {{ic|/boot}}, {{ic|/swap}}, and {{ic|/}} arrays with {{ic|mdadm}}. It is an advanced tool for RAID management that will be used to create a {{ic|/etc/mdadm.conf}} within the installation environment.<br />
<br />
Create the {{ic|/}} array at {{ic|/dev/md0}}:<br />
# mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sd[abc]3<br />
<br />
Create the {{ic|/swap}} array at {{ic|/dev/md1}}:<br />
# mdadm --create /dev/md1 --level=1 --raid-devices=3 /dev/sd[abc]2<br />
<br />
{{note|If you plan on installing a boot loader that does not support the 1.x version of RAID metadata make sure to add the {{ic|<nowiki>--metadata=0.90</nowiki>}} option to the following command.}}<br />
<br />
Create the {{ic|/boot}} array at {{ic|/dev/md2}}:<br />
# mdadm --create /dev/md2 --level=1 --raid-devices=3 --metadata=1.0 /dev/sd[abc]1<br />
<br />
==== Synchronization ====<br />
{{tip|If you want to avoid the initial resync with new hard drives add the {{ic|--assume-clean}} flag.}}<br />
<br />
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 {{ic|/proc/mdstat}} ten times per second with:<br />
# watch -n .1 cat /proc/mdstat<br />
<br />
{{tip|Follow the synchronization in another TTY terminal by typing {{Keypress|ALT}} + {{Keypress|F3}} and then execute the above command.}}<br />
<br />
Further information about the arrays is accessible with:<br />
# mdadm --misc --detail /dev/md[012] | less<br />
Once synchronization is complete the {{ic|State}} line should read {{ic|clean}}. Each device in the table at the bottom of the output should read {{ic|spare}} or {{ic|active sync}} in the {{ic|State}} column. {{ic|active sync}} means each device is actively in the array.<br />
<br />
{{note|Since the RAID synchronization is transparent to the file-system you can proceed with the installation and reboot your computer when necessary.}}<br />
<br />
==== Data Scrubbing ====<br />
<br />
It is good practice to regularly run data scrubbing to check for and fix errors, especially on RAID 5 type volumes. See the [http://en.gentoo-wiki.com/wiki/RAID/Software#Data_Scrubbing Gentoo Wiki on Data Scrubbing] for details.<br />
<br />
In short, the following will trigger a data scrub:<br />
# echo check >> /sys/block/mdX/md/sync_action<br />
<br />
The progress can be watched with:<br />
# watch -n 1 cat /proc/mdstat<br />
<br />
To stop a currently running data scrub safely:<br />
# echo idle >> /sys/block/mdX/md/sync_action<br />
<br />
It is a good idea to set up a cron job as root to schedule a weekly scrub.<br />
<br />
=== LVM installation ===<br />
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. {{ic|/}}, {{ic|/var}}, {{ic|/home}}). If you did not understand that make sure you read the [[LVM#Introduction|LVM Introduction]] section.<br />
<br />
==== Create physical volumes ====<br />
Make the RAIDs accessible to LVM by converting them into physical volumes (PVs):<br />
# pvcreate /dev/md0<br />
<br />
{{note|This might fail if you are creating PVs on an existing Volume Group. If so you might want to add {{ic|-ff}} option.}}<br />
<br />
Confirm that LVM has added the PVs with: <br />
# pvdisplay<br />
<br />
==== Create the volume group ====<br />
Next step is to create a volume group (VG) on the PVs.<br />
<br />
Create a volume group (VG) with the first PV:<br />
# vgcreate VolGroupArray /dev/md0<br />
<br />
Confirm that LVM has added the VG with: <br />
# vgdisplay<br />
<br />
==== Create logical volumes ====<br />
Now we need to create logical volumes (LVs) on the VG, much like we would normally [[Beginners Guide#Prepare Hard Drive|prepare a hard drive]]. In this example we will create separate {{ic|/}}, {{ic|/var}}, {{ic|/swap}}, {{ic|/home}} LVs. The LVs will be accessible as {{ic|/dev/mapper/VolGroupArray-<lvname>}} or {{ic|/dev/VolGroupArray/<lvname>}}.<br />
<br />
Create a {{ic|/}} LV:<br />
# lvcreate -L 20G VolGroupArray -n lvroot<br />
<br />
Create a {{ic|/var}} LV:<br />
# lvcreate -L 15G VolGroupArray -n lvvar<br />
<br />
{{note|If you would like to add the swap space to the LVM create a {{ic|/swap}} LV with the {{ic|-C y}} option, which creates a contiguous partition, so that your swap space does not get partitioned over one or more disks nor over non-contiguous physical extents:<br />
# lvcreate -C y -L 2G VolGroupArray -n lvswap<br />
}}<br />
<br />
Create a {{ic|/home}} LV that takes up the remainder of space in the VG:<br />
# lvcreate -l +100%FREE VolGroupArray -n lvhome<br />
<br />
Confirm that LVM has created the LVs with:<br />
# lvdisplay<br />
<br />
{{tip|You can start out with relatively small logical volumes and expand them later if needed. For simplicity, leave some free space in the volume group so there is room for expansion.}}<br />
<br />
=== Update RAID configuration ===<br />
Since the installer builds the initrd using {{ic|/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:<br />
# mdadm --examine --scan > /etc/mdadm.conf<br />
<br />
{{Note|Read the note in the [[RAID#Update configuration file|Update configuration file]] section about ensuring that you write to the correct {{ic|mdadm.conf}} file from within the installer.}}<br />
<br />
=== Prepare hard drive ===<br />
Follow the directions outlined the [[Beginners' Guide#Installation|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. {{ic|/dev/mapper/VolGroupArray-lvhome}}) and '''not''' the actual disks (e.g. {{ic|/dev/sda1}}).<br />
<br />
{{warning|{{ic|mkfs.xfs}} will not align the chunk size and stripe size for optimum performance (see: [http://www.linuxpromagazine.com/Issues/2009/108/RAID-Performance Optimum RAID]).}}<br />
<br />
=== Configure system ===<br />
{{warning|Follow the steps in the [[Lvm#Important|LVM Important]] section before proceeding with the installation.}}<br />
<br />
==== /etc/mkinitcpio.conf ====<br />
[[mkinitcpio]] can use a hook to assemble the arrays on boot. For more information see [[mkinitcpio#Using RAID|mkinitpcio Using RAID]].<br />
# Add the {{ic|dm_mod}} module to the {{ic|MODULES}} list in {{ic|/etc/mkinitcpio.conf}}.<br />
# Add the {{ic|mdadm_udev}} and {{ic|lvm2}} hooks to the {{ic|HOOKS}} list in {{ic|/etc/mkinitcpio.conf}} after {{ic|udev}}.<br />
<br />
=== Conclusion ===<br />
Once it is complete you can safely reboot your machine:<br />
# reboot<br />
<br />
=== Install the bootloader on the Alternate Boot Drives===<br />
Once you have successfully booted your new system for the first time, you will want to install the bootloader 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 any of the remaining drives (e.g. by switching the boot order in the BIOS). The method depends on the bootloader system you're using:<br />
<br />
==== Syslinux ====<br />
Log in to your new system as root and do:<br />
# /usr/sbin/syslinux-install_update -iam<br />
{{Note|For this to work with [[GUID Partition Table|GPT]], the {{pkg|gptfdisk}} package is needed as the backend for setting the boot flag.}}<br />
<br />
Syslinux will deal with installing the bootloader to the MBR on each of the members of the RAID array:<br />
Detected RAID on /boot - installing Syslinux with --raid<br />
Syslinux install successful<br />
<br />
Attribute Legacy Bios Bootable Set - /dev/sda1<br />
Attribute Legacy Bios Bootable Set - /dev/sdb1<br />
Installed MBR (/usr/lib/syslinux/gptmbr.bin) to /dev/sda<br />
Installed MBR (/usr/lib/syslinux/gptmbr.bin) to /dev/sdb<br />
<br />
==== Grub Legacy ====<br />
Log in to your new system as root and do:<br />
# grub<br />
grub> device (hd0) /dev/sdb<br />
grub> root (hd0,0)<br />
grub> setup (hd0)<br />
grub> device (hd0) /dev/sdc<br />
grub> root (hd0,0)<br />
grub> setup (hd0)<br />
grub> quit<br />
<br />
=== Archive your Filesystem Partition Scheme ===<br />
<br />
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 <code>sfdisk</code> tool and the following steps:<br />
# mkdir /etc/partitions<br />
# sfdisk --dump /dev/sda >/etc/partitions/disc0.partitions<br />
# sfdisk --dump /dev/sdb >/etc/partitions/disc1.partitions<br />
# sfdisk --dump /dev/sdc >/etc/partitions/disc2.partitions<br />
<br />
== Management ==<br />
For further information on how to maintain your software RAID or LVM review the [[RAID]] and [[LVM]] aritcles.<br />
<br />
== Additional Resources ==<br />
* [http://yannickloth.be/blog/2010/08/01/installing-archlinux-with-software-raid1-encrypted-filesystem-and-lvm2/ Setup Arch Linux on top of raid, LVM2 and encrypted partitions] by Yannick Loth<br />
* [http://stackoverflow.com/questions/237434/raid-verses-lvm RAID vs. LVM] on [[Wikipedia:Stack Overflow|Stack Overflow]]<br />
* [http://serverfault.com/questions/217666/what-is-better-lvm-on-raid-or-raid-on-lvm What is better LVM on RAID or RAID on LVM?] on [[Wikipedia:Server Fault|Server Fault]]<br />
* [http://www.gagme.com/greg/linux/raid-lvm.php Managing RAID and LVM with Linux (v0.5)] by Gregory Gulik<br />
* [http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml Gentoo Linux x86 with Software Raid and LVM2 Quick Install Guide]<br />
<br />
'''Forum threads'''<br />
* 2011-09-08 - Arch Linux - [https://bbs.archlinux.org/viewtopic.php?id=126172 LVM & RAID (1.2 metadata) + SYSLINUX]<br />
* 2011-04-20 - Arch Linux - [https://bbs.archlinux.org/viewtopic.php?pid=965357 Software RAID and LVM questions]<br />
* 2011-03-12 - Arch Linux - [https://bbs.archlinux.org/viewtopic.php?id=114965 Some newbie questions about installation, LVM, grub, RAID]</div>Drag0nius