Aix Online Migration PDF

8/12/2019 Aix Online Migration PDF

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Tip: Online migration of a file system to a smaller physical volume Page 2 of 6

that is done, the original oversized PV can be removed from the VG. The hdisk can then be taken

out of the Object Data Manager (ODM) using rmdev. Then, you can recycle the SAN storage for

some other use.

This procedure requires the new PV to have a suitable size and characteristics for adding to the

existing VG. It must be large enough to hold all the data that is on the original PV (the used PPs).The procedure also assumes that there is no logical volume (LV) striping that would restrict the

ability to run a mirror of a logical volume using mklvcopy.

For this exercise, there is a VG called datavgwith a 50 GB PV. The lspvcommand shows the total

size of the PV as well as the free and used PPs (see Listing 1).

Listing 1. Displaying physical volume characteristics

# lspv hdisk1

PHYSICAL VOLUME: hdisk1 VOLUME GROUP: datavg

PV IDENTIFIER: 00cb07a45a12b4ca VG IDENTIFIER 00cb07a400004c00000001345a26db3e

PV STATE: activeSTALE PARTITIONS: 0 ALLOCATABLE: yes

PP SIZE: 512 megabyte(s) LOGICAL VOLUMES: 1

TOTAL PPs: 99 (50688 megabytes) VG DESCRIPTORS: 2

FREE PPs: 0 (0 megabytes) HOT SPARE: no

USED PPs: 99 (50688 megabytes) MAX REQUEST: 256 kilobytes

FREE DISTRIBUTION: 00..00..00..00..00

USED DISTRIBUTION: 20..20..19..20..20

MIRROR POOL: None

There is a single enhanced journaled file system (JFS2) called/scratchthat has more than 35 GB

free of its 49.50 GB allocation. This file system was created with an INLINE JFS2 log:

# df -gI /scratch

Filesystem GB blocks Used Free %Used Mounted on

/dev/scratchlv 49.50 14.20 35.30 29% /scratch

The fine print

This solution applies to LVs that are not striped at the LVM level. LVM striping introduces

its own restrictions that are beyond the scope of this article. The file system in this example

uses an INLINE JFS2 log.

The solution here also assumes that there is sufficient storage to create a new SAN LUN

of similar performance and redundancy to the originalso that the end result will not affect

system response times. The new LUN should have sufficient space to fit the used PPs from

the original, larger LUN.

Reduce the file system

Because the file system is using less than one third of its allocation, its total disk allocation can be

reduced. You can reduce the file system size using chfs. The following command reduces it by 30

GB:

# chfs -a size=-30G /scratch

Filesystem size changed to 40894464

Inlinelog size changed to 78 MB.


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The total disk allocation for the file system has been reduced to 19.50 GB:

# df -gI /scratch

Filesystem GB blocks Used Free %Used Mounted on

/dev/scratchlv 19.50 14.08 5.42 73% /scratch

This process has freed up some PPs on the PV, as the lspvcommand in Listing 2shows.

Listing 2. lspv showing free physical partitions

# lspv hdisk1

PHYSICAL VOLUME: hdisk1 VOLUME GROUP: datavg

PV IDENTIFIER: 00cb07a45a12b4ca VG IDENTIFIER 00cb07a400004c00000001345a26db3e

PV STATE: active

STALE PARTITIONS: 0 ALLOCATABLE: yes

PP SIZE: 512 megabyte(s) LOGICAL VOLUMES: 1

TOTAL PPs: 99 (50688 megabytes) VG DESCRIPTORS: 2

FREE PPs: 60 (30720 megabytes) HOT SPARE: no

USED PPs: 39 (19968 megabytes) MAX REQUEST: 256 kilobytes

FREE DISTRIBUTION: 00..01..19..20..20

USED DISTRIBUTION: 20..19..00..00..00MIRROR POOL: None

Add a smaller physical volume to the volume group

The next step is to add a new, smaller PV to the existing VG. This PV should have at least the

same redundancy and input/output (I/O) performance as the original, larger PV. For example, it

should be of an equivalent Redundant Array of Independent Disks (RAID) array. Any other tuning

characteristicssuch as queue depth should be set to ensure that the system performance is

comparable to the original, larger PV.

Create a new LUN, and allocate it to the AIX logical partition (LPAR). In this example, the new LUNis 20 GB:

# cfgmgr

The output of the lspvcommand shows that the new disk is called hdisk2(see Listing 3) and it

does not yet belong to a VG.

Listing 3. Listing the new disk

# lspv

hdisk0 00c5a47e3f356f3c rootvg active

hdisk1 00cb07a45a12b4ca datavg active

hdisk2 none None

You can view the size of the disk even before it is added to a VG using the getconfcommand. This

reports the size in MB:

# getconf DISK_SIZE /dev/hdisk2

20480

Add the disk to the existing VG using the extendvgcommand:


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# extendvg datavg hdisk2

0516-1254 extendvg: Changing the PVID in the ODM.

Mirror or migrate the logical partitions to a new physical volume

You can mirror the LV to the new PV, and then remove the copy from the original PV after all thePPs have been synchronised between the two PVs.

mklvcopy -k scratchlv 2

Migrate instead of mirror

Instead of mirroring, you can migrate the LV using migratepv. Refer to Resourcesfor a link

to more information.

There are other options for mklvcopy. For example, you can postpone the synchronization until

a quieter time. You can also specify the disk allocation policy. The official documentation for

mklvcopyhas the necessary details (refer to Resources).

Remove the copy from the original physical volume

When the synchronization is complete, you can remove the copy from the original PV using

rmlvcopy. Be sure to specify the PV that has the copy you want to remove.

rmlvcopy scratchlv 1 hdisk1

You can use the lspvcommand to confirm that there are no more used PPs on the original PV. If

there are still some PPs in use, you can list the LVs on the PV using lspv -lPVNAME.When you

are sure that all the PPs have been moved to other PVs, the original PV can be removed from the

VG using reducevg:

reducevg datavg hdisk1

You should be able to remove the original larger PV from the ODM using rmdev:

rmdev -d -l hdisk1

Finally, you can remove the LUN or allocate it for some other use.

Cutting out outages

As you can see, the LVM features allow you to move data aroundeven to smaller diskswithout

unnecessary user impact. By taking advantage of the LVM mirroring and migration capabilities,

you can keep your system up and still recover the much-needed storage space if it has been over-

allocated.


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About the author

Anthony English

Anthony English is an independent contractor from Sydney, Australia. He has worked

on AIX systems since 1991 and writes the IBM developerWorks blog, AIX Down

Under. He is also recognized as an IBM Champion for Power Systems. You can reach

Anthony at [email protected].

Copyright IBM Corporation 2012

(www.ibm.com/legal/copytrade.shtml)

Trademarks

(www.ibm.com/developerworks/ibm/trademarks/)
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