Hp education services education.hp.com 50 LVM Problems Version C.00 H4264S Module 6 Slides

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LVM Problems

Version C.00H4264S Module 6 Slides

2 © 2001 Hewlett-Packard Company

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LVM — Logical Volume Manager

LVM provides:• Disk grouping• Logical partitioning• Ability to span disk drives• Bad block replacement• Disk mirroring (optional product)

Logical Volumes

Physical Volume

B B S

Physical Extent

SS

S RU

R

VVVOO O

TT

T

H H

H

Volume Group

B = boot V = varS = swap O = optR = root T = tmpU = usr H = home


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LVM Disk Layout

User Data Area

Bad Block Relocation Pool

Volume Group Reserved Area

LIF Volume

Boot Data Reserved Area

Physical Volume Reserved Area

LIF Header (8 blocks)Physical Volume Reserved Area

Volume Group Reserved

User Data Area


Bootable Disk Non-bootable Disk

Area


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Physical Volume Reserved Area (PVRA)The PVRA stores information about the LVM diskconfiguration (starting addresses and sizes):

• LVM identification field, signifying the LVM record is present and valid

• Unique physical volume ID, checked by LVM when it generates new physical volumes

• Physical volume number

• Last physical sector number

• Size of each physical extent on the LVM disk

• The locations of the other LVM data structures on the disk

• The start of the user data

Physical Volume Reserved Area

VGRA

User Data Area



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Volume Group Reserved Area (VGRA)The volume group reserved area (VGRA)

holdsdata describing the volume group that

containsthe disk:

• Volume Group Descriptor Area (VGDA)– How many LVs are in the VG?– How many PVs are in the VG?– PE to LE mapping

• Volume Group Status Area (VGSA)– Tracks validity and availability of PVs– Tracks current state of each PE

PVRA

Volume GroupReserved Area

User Data Area



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LVM Repair Tools — Overview

Primary Commands:• vgcfgrestore• vgscan• vgexport• vgimport

Other Commands:

• lvlnboot• ISL> hpux -lm• ISL> hpux -lq


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Backing Up and Restoring LVM Configuration Information

/sbin/vgcfgbackup

/sbin/vgcfgrestore

/usr/bin/fbackup

/usr/bin/frecover

Physical VolumeReserved Area

Volume GroupReserved Area

User Data Area



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LVM Recovery after Disk Replacement

lvol1

lvol2

lvol2

lvol3

lvol4

lvol4

lvol5

c2t5d0 c2t3d0c2t4d0

lvol1

lvol2

NewDisk

lvol4

lvol5

c2t5d0 c2t3d0c2t4d0

# vgchange -a n /dev/vg02

# vgcfgrestore -n /dev/vg02 /dev/rdsk/c2t4d0

# vgchange -a y /dev/vg02


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Corrupted PVRA/VGRA Structures on the Boot Disk

• LVM maintenance mode puts the system into single-user mode.

• LVM maintenance mode is used to repair damaged LVM data structures.

ISL> hpux -lm

ISL> hpux -lm (56/52.6.0;0)/vmunix

If the PVRA or VGRA structures are corrupted, the volume group cannot be activated.

A special way to boot the system (LVM maintenance mode) can be used to bypass the normal LVM structures.


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LVM Maintenance Mode

LVM Maintenance Mode

• The /dev/vg00 volume group is not activated.

• The root and boot logical volumes are mounted, even though the vg00 volume group is not active.

• This mode allows the LVM header information to be restored to the boot disk:

# vgcfgrestore -n /dev/vg00 /dev/rdsk/c0t6d0

# reboot -n

CAUTION: While in LVM maintenance mode, do not bring the system into multiuser mode.


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The LABEL File

LABEL File

• Contains pointers to the starting points and sizes of boot relevant logical volumes.

• Resides in the LIF volume.

• Information stored within LABEL is used by the secondary loader to load the operating system.

# lifls -l /dev/rdsk/c0t6d0 User Data Area


VGRA

LIF Volume

BDRA

PVRA

LIF Header (8 blocks)

Bootable Disk


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Boot Data Reserved Area (BDRA)

The BDRA contains the following recordsabout the system's root logical volumes:

• Root volume group ID• Number of disks in root volume group• A list of hardware addresses of the LVM disks in the root volume group• Information needed to select the correct logical volumes for boot, primary swap, and dump

The operating system uses the information in the BDRA to activate the root volume group and mount the root file system.

User Data Area


VGRA

LIF Volume

BDRA

PVRA



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Corrupt or Missing LABEL File or BDRA

• The system will not boot.

• To recover, the system must be booted into LVM Maintenance mode or to the recovery shell.

• A command called lvlnboot is needed to fix the problem.

If the LABEL file or BDRA is corrupt or missing:

User Data Area


VGRA

LIF Volume

BDRA

PVRA



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The lvlnboot Command

lvlnboot:

• Used to update a corrupted LABEL file or BDRA with valid data.

• The syntax of the command is:

• Examples of the command:# lvlnboot -b /dev/vg00/lvol1

# lvlnboot -r /dev/vg00/lvol3

# lvlnboot -s /dev/vg00/lvol2

# lvlnboot -d /dev/vg00/lvol2

lvlnboot [-b|-r|-s|-d] lvol_name


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Using the Recovery Shell to Repair Damage The recovery shell can also be used to repair a corrupted LABEL file or BDRA. The procedure is:

1. Boot from the support media.2. From the Recovery menu, select Exit to shell (recovery shell).3. From the Recovery shell, execute the following commands:

“Recovery shell to the rescue”

# chroot_lvmdisk# cd /ROOT# chroot /ROOT /sbin/sh# vgchange -a y /dev/vg00# lvlnboot -b /dev/vg00/lvol1. . .# reboot


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Booting without Quorum

Booting without quorum allows your system to come up when:• The root volume group does not meet quorum requirement.• The disk containing the root file system is functional.

ISL> hpux -is -lq

Boot Area

lvol1

mirrorcopies

lvol2

lvol3

lvol4

/dev/vg00 Crash!

Boot Area


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Recovering an lvmtab File

The /etc/lvmtab file:• Lists all volume groups and the physical volumes that

are associated with each volume group• Can be viewed using the strings command• Contents used by LVM commands• Can be recreated using the vgscan command

For example:

# mv /etc/lvmtab /etc/lvmtab.back

# vgscan -pv

# vgscan -v

# strings /etc/lvmtab


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Last Resort

# vgchange -a n /dev/vg02# vgexport -m /tmp/mapfile /dev/vg02

# mkdir /dev/vg02# mknod /dev/vg02/group c 64 0x020000# vgimport -v -m /tmp/mapfile /dev/vg02 \ /dev/dsk/c3t4d0 /dev/dsk/c4t5d0# vgchange -a y /dev/vg02

# strings /etc/lvmtab

# vgcfgbackup vg02

If the volume group still cannot be repaired, as a last resort, try exporting and importing the volume group:

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Hp education services education.hp.com 50 LVM Problems Version C.00 H4264S Module 6 Slides