Saturday, February 25, 2012

LVM basics

I spent a few hours with iSCSI SAN disks (EqualLogic) and Linux Logical Volume Manager (LVM). The abstraction is even deeper than that, because Linux at work is running under VMware, so it is really VMware talking to the SAN and presenting a SCSI disk to Linux. Since I only get into the LVM weeds a couple of times a year, I thought it would be helpful to list the steps I took to get usable disk space under Linux starting with the raw disk space.

Step One - create a new partition

Create a new partition with FDISK or PARTED. Mark the partition type hex 8E for LVM. In my case, the SCSI disk appeared as /dev/sdb and the partition using all space became /dev/sdb1. LVM is capable of using a raw device (no partition type), but I stayed in familiar partitioning territory.

Step Two - create LVM physical volume

pvcreate /dev/sdb1

Step Three - create LVM volume group in the physical volume

vgcreate new_volume_group /dev/sdb1

Step Four - create LVM logical volume in the volume group

lvcreate --name new_logical_volume --size 100G new_volume_group

Step Five - create a file system on the logical volume

mkfs -t ext4 /dev/mapper/new_volume_group-new_logical_volume
Note: Linux device mapper automatically creates a symlink to the disk in /dev/mapper using the volume group and logical volume names. If you choose more meaningful names than the example, the name won't look so awful.

Step Six - turn off automatic file system checks (optional)

tune2fs -c 0 /dev/mapper/new_volume_group-new_logical_volume

Step Seven - add mount point in /etc/fstab

Once the mount point is list in fstab, mount it manually and it is ready to use.

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