papyri/md/reducing_the_root_lv.md

Reducing the root LV

Contents

• Overview
• Procedure
  • Without lvresize -r flag
  • With lvresize -r flag

Overview

Reducing the root logical volume requires booting into a rescue environment that has the LVM utilities.

Some rescue images have a version of the LVM utilities that were released missing a critical shim needed to resize filesystems using the -r flag to lvresize. It may or may not be necessary to resize the filesystem as a separate step, both are outlined.

Procedure

Given this current configuration of a 250G boot volume:

Mount	Size	VG / LV
/boot	250M	n/a
/tmp	2G	vglocal / lvtmp
swap	2G	vglocal / lvswap
/	remainder	vglocal / lvroot

We'll reduce the root (/) volume and grow swap and /tmp to end up with:

Mount	Size	VG / LV
/boot	250M	n/a
/tmp	4G	vglocal / lvtmp
swap	32G	vglocal / lvswap
/	remainder	vglocal / lvroot

Without lvresize -r flag

##
## DO NOT MOUNT ANY FILESYSTEMS DURING RESCUE BOOT
##

# activate all LVM
lvm vgchange -a y

# fsck the filesystems; it's normal to get a message about a time error that needs fixed
fsck -fC /dev/vglocal/lvroot
fsck -fC /dev/vglocal/lvtmp

# shrink the ext3/4 root far below what we need
resize2fs -p /dev/vglocal/lvroot 200G

# reduce the root LV a bit above what we just resized (+5GB)
lvm lvresize /dev/vglocal/lvroot --size 205G

# increase swap and tmp LVs
lvm lvresize /dev/vglocal/lvswap --size 32G
lvm lvresize /dev/vglocal/lvtmp --size 4G

# re-grow the root LV back to max space
lvm lvresize -l +100%FREE /dev/vglocal/lvroot

# re-grow the / and /tmp ext3/4 to fill the increased LVs
resize2fs -p /dev/vglocal/lvroot
resize2fs -p /dev/vglocal/lvtmp

# fsck the filesystems again
fsck -fC /dev/vglocal/lvroot
fsck -fC /dev/vglocal/lvtmp

# rescue image 'mkswap' is sometimes not able to see a large swap
reboot

# finally, make a new swap signature that sees the whole LV
swapoff /dev/vglocal/lvswap
mkswap /dev/vglocal/lvswap
swapon /dev/vglocal/lvswap

With lvresize -r flag

##
## DO NOT MOUNT ANY FILESYSTEMS DURING RESCUE BOOT
##

# activate all LVM
lvm vgchange -a y

# fsck the filesystems; it's normal to get a message about a time error that needs fixed
fsck -fC /dev/vglocal/lvroot
fsck -fC /dev/vglocal/lvtmp

# reduce the size of LV root a tad more than we need
lvm lvresize -r /dev/vglocal/lvroot --size 200G

# increase swap and tmp LVs
lvm lvresize /dev/vglocal/lvswap --size 32G
lvm lvresize /dev/vglocal/lvtmp --size 4G

# re-grow the root LV back to max space
lvm lvresize -r -l +100%FREE /dev/vglocal/lvroot

# fsck the filesystems again
fsck -fC /dev/vglocal/lvroot
fsck -fC /dev/vglocal/lvtmp

# rescue image 'mkswap' is sometimes not able to see a large swap
reboot

# finally, make a new swap signature that sees the whole LV
swapoff /dev/vglocal/lvswap
mkswap /dev/vglocal/lvswap
swapon /dev/vglocal/lvswap