Working with Linux volumes on vSphere

Modern Linux distributions running on VMware vSphere are capable for dynamic storage management, it is possible to create new file systems or extend existing without need to stop services and reboot servers. Here are some examples how to that, these methods work at least on Red Hat and CentOS 5.x distributions.

Things to consider with Linux volumes

If your intention is to use all of your new disk for single file system I recommend that you do not use partitioning, use a plain disk as LVM physical volume instead, it simplifies managing volumes a lot. You could also chose not to use LVM and format new disk as is with ext3 but I do not recommend that, using LVM has many benefits which I might cover on some later articles.

If you need to use partitioning you should be aware of following caveats

1. To avoid performance penalty from file system misalignment you need to match beginning of new partition with underlying storage device using fdisk expert commands
2. Using partitions makes extending file systems much more complicated compared to using plain disks instead

If you fail to align file system properly with your storage, you can lose up to 15% of your available IOPS.

Attach new disks without reboot

After new virtual disk have been added to virtual machine you need to rescan new disks in Linux. Scan new disks with command below, replace “host0″ with SCSI controller ID you added disks to

# echo "- - -" > /sys/class/scsi_host/host0/scan

use dmesg command to check what new devices have been added, watch for “Attached scsi disk” message

# dmesg | tail -n 10 | grep Attached
sd 0:0:1:0: Attached scsi disk sdb

Now create LVM Physical Volume, Volume Group, Logical Volume and file system on your new disk

# pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created
# vgcreate VolGroup01 /dev/sdb
  Volume group "VolGroup01" successfully created
# lvcreate -n LogVol00 -l+100%VG VolGroup01
  Logical volume "LogVol00" created
# mkfs.ext3 /dev/VolGroup01/LogVol00

Or if you know that you don’t need LVM you can simply format plain disk with

# mkfs.ext3 /dev/sdb

Your new volume is ready for mounting.

Resizing existing disks

After virtual disk have been resized you need to rescan changes in Linux. You must know SCSI ID of disk changed, replace 0:0:1:0 in example below with correct SCSI ID

# echo 1 > /sys/bus/scsi/devices/0\:0\:1\:0/rescan

use dmesg to check that resize is successful, watch for “capacity change” message

# dmesg | tail -n 10 | grep change
sdb: detected capacity change from 8589934592 to 17179869184

if LVM is not used resizing file system can be done with command

# resize2fs /dev/sdb

Other ways proceed to extend LVM volume

Extending LVM volume and file system, easy way with no partitions

Rescan LVM physical volume size change with pvresize, replace sdb with correct device

# pvresize /dev/sdb

Extend LVM logical volume to new full size of volume group

# lvextend -l+100%VG /dev/VolGroup01/LogVol00

Now you can resize mounted ext3 file system

# resize2fs /dev/VolGroup01/LogVol00

And you are done

Extending LVM volume and file system, hard way with partitions in use

You cannot resize LVM physical device on partition without reboot, when using single disk your only option is to create new partition on space created by extending disk and use partprobe command to reload partition table without need to reboot. You could also create new disk and extend Volume Group to that.

Create a new partition to existing disk

# fdisk /dev/sdb
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (3134-3916, default 3134):
Using default value 3134
Last cylinder or +size or +sizeM or +sizeK (3134-3916, default 3916):
Using default value 3916

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

Run partprobe to reload partition table

# partprobe /dev/sdb

Create new LVM physical volume to new partition

# pvcreate /dev/sdb2

Add new physical volume to existing Volume Group

# vgextend VolGroup01 /dev/sdb2

Extend Logical Volume up to maximum size of Volume Group

# lvextend -l+100%VG /dev/VolGroup01/LogVol00

Finally you can resize mounted ext3 file system

# resize2fs /dev/VolGroup01/LogVol00

Done. See how much work there is when using partitions? There is absolutely no point at all to create partition table for standard ext3 file system when intention is to use whole disk for single file system.