Gentoo LVM2 installation

Follow the handbook, but with the following amendments to chapter 4. Preparing the Disks:

Use fdisk as described in the handbook, but use the partition scheme mentioned above as an example. It is only an example, adapt it to your own needs.

Create a small physical /boot partition (sda1). In this example, /boot will be not managed by LVM2. This partition will contain your bootloader and your kernel(s). A 64MB partition should be well enough for quite a few kernel generations.

Create a swap partition (sda2).

Create a / (root) partition (sda3). If you are interested in trying to put your root partition under LVM management (which we do not recommend), see the resources section at the end of this guide for a link to a mini-howto on how to do this. The size of the root partition need not be large if you will keep /opt /usr /home /var and /tmp in an LVM2 Volume Group (vg). In this case, 1GB should be sufficient. Note however that, if you have /usr or /var in an LVM2 volume group, you will need to boot the system with an initramfs.

It is not recommended to put the following directories in an LVM2 partition: /etc, /lib, /mnt, /proc, /sbin, /dev, and /root. This way, you would still be able to log into your system (crippled, but still somewhat usable, as root) if something goes terribly wrong. Also exclude /usr and /var from LVM2 if you do not want to boot with an initramfs.

Assuming the /boot, swap and root partitions do not use the whole physical disk, create a fourth partition on this disk and set it to type 8e (Linux LVM). If you have more physical drives you would like to use with LVM, create one partition on each and give them the same type (8e).

Considering the huge size of current disks, you might consider splitting your hard disks into smaller partitions instead of creating a big partition that will be added to an LVM2 volume group in one block. LVM2 makes it easy to extend your volumes after all. This leaves you some unallocated partitions you might need to use outside of an LVM2 group. In short, don't use your disk space until you know you need it. As an example, one contributor had split his 160 Gb hard disk into 8 partitions of 20 Gb each.

Create the filesystems on /dev/sda1 and /dev/sda3, and create and activate the swap on /dev/sda2 as described in the handbook.

Start the lvm service.

# rc-config start lvm

It is recommended to add the lvm service to the boot runlevel. This way LVM2 will be activated each time the system boots.

# rc-config add lvm boot

Before scanning and activating LVM, you might want to edit /etc/lvm/lvm.conf to exclude some devices. By default, LVM2 will scan all devices, even your CDROM which can generate error messages. In the following example, the line that allows scanning of all devices is replaced by one that rejects every device but our two SATA disks.

(Avoid scanning all devices but our disks)
# nano -w /etc/lvm/lvm.conf
(Look for the following line)
    filter = [ "a/.*/" ]
(Replace it with the following one to scan
/dev/sda and /dev/sdb and reject anything else)
    filter = [ "a|/dev/sd[ab]|", "r/.*/" ]
(Save the file and quit nano)
# vgscan
  Reading all physical volumes.  This may take a while...
  No volume groups found
(Make any previously set up volume groups available)
# vgchange -a y

Prepare the partitions.

# pvcreate /dev/sda4 /dev/sdb1
  No physical volume label read from /dev/sda4
  Physical volume "/dev/sda4" successfully created
  No physical volume label read from /dev/sdb1
  Physical volume "/dev/sdb1" successfully created

Setup a volume group. A volume group is the result of combining several physical units into a single logical device.

In our example, /dev/sda1, /dev/sda2 and /dev/sda3 are the /boot, swap and root partitions so we need to combine /dev/sda4 and /dev/sdb1. It can be done with a single command, but, as an example, we will create our volume group and extend it.

(Create a volume group named vg)
# vgcreate vg /dev/sda4
  /etc/lvm/backup: fsync failed: Invalid argument (Ignore this warning)
  Volume group "vg" successfully created
(Extending an existing volume group)
# vgextend vg /dev/sdb1
  /etc/lvm/backup: fsync failed: Invalid argument (Ignore this warning, again and later as well)
  Volume group "vg" successfully extended

Create the logical volumes. Logical volumes are the equivalent of partitions you would create using fdisk in a non LVM2 environment. In our example, we create the following partitions:

/usr10 GB/home5 GB/opt5 GB/var10 GB/tmp2 GB

Directory	Size

Since we are going to use LVM2, we should not worry too much about partition sizes because they can always be expanded as needed.

As Terje Kvernes commented, it is easier to increase the size of a partition then to shrink it. You might therefore want to start with smaller partitions and increase their size as needed.

# lvcreate -L10G -nusr  vg
  Logical volume "usr" created (Further similar messages not displayed)
# lvcreate -L5G  -nhome vg
# lvcreate -L5G  -nopt  vg
# lvcreate -L10G -nvar  vg
# lvcreate -L2G  -ntmp  vg
(As an example, let's extend a logical volume with 5 extra Gbytes)
# lvextend -L+5G /dev/vg/home

Create filesystems on the logical volumes the same way you would on a regular partition. We use ext3 on the logical volumes but any filesystem of your choice will work:

# mke2fs -j /dev/vg/usr
# mke2fs -j /dev/vg/home
# mke2fs -j /dev/vg/opt
# mke2fs -j /dev/vg/var
# mke2fs -j /dev/vg/tmp

Mount your partitions as described in the handbook and mount your LVM2 logical volumes as if they were partitions. Replace the usual /dev/sdxx with /dev/vg/logical_volumename.

(Make sure you have mounted your root partition as described in the handbook first)
# mkdir /mnt/gentoo/usr
# mount /dev/vg/usr /mnt/gentoo/usr
# mkdir /mnt/gentoo/home
# mount /dev/vg/home /mnt/gentoo/home
# mkdir /mnt/gentoo/opt
# mount /dev/vg/opt /mnt/gentoo/opt
# mkdir /mnt/gentoo/var
# mount /dev/vg/var /mnt/gentoo/var
# mkdir /mnt/gentoo/tmp
# mount /dev/vg/tmp /mnt/gentoo/tmp

The rest of the installation handbook is mostly unchanged so we shall not walk you through it again except to point out differences.

When configuring your kernel, make sure to configure your kernel to support LVM2. Select the LVM2 module as follows:

Device Drivers  --->
 Multiple devices driver support (RAID and LVM) --->
   [*] Multiple devices driver support (RAID and LVM)
   < >   RAID support
   <M>   Device mapper support

The compiled module is called dm-mod.ko

Also build an initramfs if you have /usr or /var on an LVM-based partition. Don't forget to edit your boot loader to boot the system with the initramfs and add in dolvm as a boot parameter.

# emerge genkernel
# genkernel --lvm --install initramfs
# nano -w /boot/grub/grub.conf
(...)
title Gentoo Linux
root (hd0,0)
kernel /kernel-3.2.2-gentoo-r5 root=/dev/sda1 dolvm
initrd /initramfs-genkernel-x86_64-3.2.2-gentoo-r5

Now, install the lvm2 package.

Make sure your /usr/src/linux link points to the kernel sources you are using because the lvm2 ebuild depends on the device-mapper ebuild which will check the presence of a required source file under /usr/src/linux/include/linux.

# emerge lvm2

Edit /etc/lvm/lvm.conf as described earlier. The file you previously edited is part of your installation environment and will disappear after the next reboot. This time, you edit the real one inside your new Gentoo install.

When editing your /etc/fstab file, follow the handbook and add your LVM2 logical volumes as needed. Again, here are a few lines needed for our example:

/dev/sda1     /boot   ext3    noauto,noatime 1 2
/dev/sda2     none    swap    sw             0 0
/dev/sda3     /       ext3    noatime        0 1
# Logical volumes
/dev/vg/usr   /usr    ext3    noatime        0 2
/dev/vg/home  /home   ext3    noatime        0 2
/dev/vg/opt   /opt    ext3    noatime        0 2
/dev/vg/var   /var    ext3    noatime        0 2
/dev/vg/tmp   /tmp    ext3    noatime        0 2

When you reach the end of the installation part of the handbook, don't forget to umount all your LVM2 logical volumes as well and for a good measure run the following command before you reboot:

# vgchange -a n

Restart your machine and all partitions should be visible and mounted.