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AIX Logical Volume Manager

Redbooks IBM Links Recommended Links   quick_reference.l
what disks are in the root volume group How many disks are on the system Create a volume group Add a disk to the root volume group Make sure the disks are in an active state Mirror the logical volumes Create the boot image on the new disk
Extend the size of filesystem Remove a file system JFS mksysb Command Aix JFS2 snapshots Humor Etc

what disks are in the root volume group

# lsvg -p rootvg
hdisk0            active            546         186         00..00..00..77..109

Now let's see how many disks are on the system

# lspv
hdisk0          00cf4f5d02a3c139                    rootvg          active
hdisk1          00cf4f5da1ca9590                    none 
Create a volume group:
  1. lsdev -C -c disk  -> lists available disks (and the hdisk#) on the server
  2. mkvg -y "<VG_NAME>" hdisk#  --> creates the volume group on the named hard disk
  3. varyonvg <VG_NAME>  --> activates the volume group

Add a disk to the root volume group (extend the volume group) extendvg <vg> <disk#>

# extendvg -f rootvg hdisk1

Make sure the disks are in an active state

# lspv
hdisk0          00cf4f5d02a3c139                    rootvg          active
hdisk1          00cf4f5da1ca9590                    rootvg          active

 Mirror athe logical volumes that exist on a given volume group

# /usr/sbin/mirrorvg rootvg hdisk0 hdisk1

0516-1124 mirrorvg: Quorum requirement turned off, reboot system for this
to take effect for rootvg.
0516-1126 mirrorvg: rootvg successfully mirrored, user should perform
bosboot of system to initialize boot records. Then, user must modify
bootlist to include: hdisk0 hdisk1.
Check to see if  all of the logical volumes in a volume group are mirrored Mirror a logical volume after the fact

Create the boot image on the new disk and put it on the bootlist

# bosboot -ad /dev/hdisk1

bosboot: Boot image is 25166 512 byte blocks.
bootlist -m normal hdisk0 hdisk1

Confirming that all of the volumes are on the boot image
# lsvg -p rootvg
hdisk1            active            546         186         00..00..00..77..109
hdisk0            active            546        186         00..00..00..77..109

Logical Volume Manager (LVM) Commands for AIX

Filesystem Procedures

Procedure to create a filesystem using JFS:
Extend the size of filesystem :
  1. "df" to see the filesystem, it's current size, % utilization and the name of it's logical volume
  2. "lslv <logical_volume>" to show information about the logical volume including it's volume group name.
  3. "lsvg <volume_group>" to show information about the volume group, including number of free pp's and the pp size
  4. If there are not enough free pp's then see below for procedure to add a disk to a volume group.
  5. "chfs -a size= +4194304 <MOUNT_POINT>" to grow the filesystem by 2 GB (4194304=2*1024*1024*1024/512)
  6. df" shows the file system's current size is 2 GB more than before.
Troubleshooting extending the size of a filesystem using JFS: Remove a file system
  1. Unmount the filesystem
  2. Remove the logical volume "rmlv <lv_name>"
  3. Remove the filesystem information from /etc/filesystems
Procedure to reduce the size of a file system - shareold is 8mb and needs to be reduced to 4mb
  1. Create the file system
    1. crfs -v jfs -m /usr/sharenew -g rootvg -a size=8192
    2. this makes a logical volume in the root volume group of 4MB that uses jfs
  2. Mount the volume
    1. mount /usr/sharenew
  3. Move the files from the old file system (/usr/shareold)
    1. cd /usr/shareold
    2. tar cf - | (cd /usr/sharenew; tar xvf -)
    3. cd
  4. Unmount the file systems
    1. umount /usr/sharenew
    2. umount /usr/shareold
  5. Remove the old file system and it's logical volume
    1. rmfs /usr/shareold
    1. chfs -m /usr/shareold /usr/sharenew
  7. Mount the new filesystem
    1. mount /usr/shareold
  8. Delete the temporary mount point
    1. rmdir /usr/share

Logical Volume Procedures

Create a logical volume and filesystem in a volume group:
  1. lsvg to determine the size of the PP
  2. lslv in similar logical volumes to determine if mirroring is in effect
  3. Calculate the number of PPs needed for the logical volume
    1. bc
    2. scale=2
    3. <size of lv in MB>/<size of PP in MB>
    4. quit
  4. mklv -y  "<LV_NAME>" <VG_NAME> <# of LPS>  --> creates the logical volume
  5. crfs -v jfs -d <LV_NAME> -m /<MOUNTPOINT> -A yes   --> makes the filesystem, creates the mountpoint and puts it in /etc/filesystems
  6. mount /<MOUNTPOINT>  --> mounts the new fileystem
  7. df /<MOUNTPOINT>  --> verifies the mount and the size of the new filesystem
  8. Check the ownership and permissions of the new mount point
  9. If mirroring is in effect, then mirror this logical volume to another disk (original and 1 mirror):


Volume Group Procedures

Procedure to mirror the rootvg:
  1. lspv  --> determine the hdisk#
  2. extendvg rootvg hdisk<number>  --> add the hdisk to the volume group
  3. lspv  -->  verify that the hdisk has been successfully added to the volume group
  4. chvg -Q 'n' rootvg  -->  change the quorum so that the vg will stay active if one of the mirrors fail
  5. mirrorvg -S -c 2 rootvg  --> mirror all of the logical volumes in the volume group
  6. lsvg -l rootvg  --> verify successful mirroring (pps will appear "stale" until synchronization is complete).
  7. bosboot -a  -->  update the boot image information
  8. bootlist -m normal -o hdisk0 hdisk1  --> create a new bootlist
  9. bootlist -m normal -o  --> verify the bootlist is correct
Procedure to increase the number of LP's available
Assume we receive an error that the maximum number of LP's had been exceeded, and the maximum number of LP's defined was 1100:
  1. "lsvg <volume_group>" to show the total PP's available in the volume group =1250
  2. "lsvg -l <volume_group>" to show the total PP's used in all logical volumes in that volume group (showed sys1log, the jfs log was using 2 PP's)
  3. "chlv -x 1248 <logical_volume>" to change the maximum number of LP's from 1100 to 1248 (1250 PP's in the volume group - 2 PP's used by the jfs log  = 1248 available)

Physical Disk Procedures

Procedure to find disks/vpaths that are unallocated Procedure to make a new lun available to AIX
Procedure to list the PVs in a volume group:


Logical Volume Manager

During the early stages of UNIX®, the management of physical disks was always a daunting task because of the restrictions on allocating the actual physical space. You'd have to define physical partitions, and each physical partition would actually be of a fixed size. Additionally, a physical disk could only have eight physical partitions, so the customer had to select the correct size of each partition before installing the system.

A major restriction of the physical partition was that each partition had to be contiguous; meaning you could not span multiple drives. What evolved from this messy picture was a new, flexible technique to manage the allocation, known as logical volumes. Here are some of the benefits:

AIX and Solaris offer different methods for using logical volumes. With Solaris, it does not come ready out of the box. You need to determine which LVM to use, and decide whether or not to use SVM or VERITAS. While VERITAS offers the VERITAS Foundation suite for AIX 5L™, it is typically not used in AIX environments, as it is not necessary. VERITAS Volume Manager (VxVM) is a storage management subsystem that enables you to manage physical disks as logical devices called volumes. It is important to reiterate that this product is third-party software, and you will pay handsomely for it.

The LVM has been a feature of the AIX operating system since Version 3, and it is installed automatically with the operating system. Table 1 helps lay out some of the differences between AIX and VERITAS, and it also compares the commands (for the complete table, see Resources). While the version numbers might be different, the concepts and commands remain the same.


Figure 1 illustrates how the physical disk relates to the actual logical partitions.


Recommended Links

Transition from Solaris to AIX

AIX File Structure Volume Logical Tips



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