IBM Support

Migrating Load Source disk unit to a smaller size

How To


Starting at 7.2 (V7R2) with Technology Refresh 2 (TR2) or 7.3 (V7R3) with any Technology Refresh, IBM i may allow migrating the Load Source (LS) disk unit to a smaller size by using the following procedure to move data off of the LS and check the minimum size.

Note: Earlier releases of IBM i only supported migrating the LS to the same size or larger unit.
Note: Base 7.4 (V7R4) and higher supports migrating to smaller units using the copy disk unit data function in DST - this document is not needed.


  1. Check the current minimum size the LS can be copied to
    1. Run STRSST command from IBM i command line
    2. Log into System Service Tools with Service Tools user ID and password
    3. Option 1 - Start a service tool
    4. Option 4 - Display/Alter/Dump
    5. Option 1 - Display/Alter storage
    6. Option 2 - Licensed Internal Code (LIC) data
    7. Option 14 - Advanced analysis
    8. On the top line type option 1 and command DUMPFSMAPINFO then press enter
    9. On the options line type -D and press enter
    10. Look for first line that says "High Water Mark:" and write down the hex number on that same line image-20190605121252-1
    11. Convert the hex number to decimal (example:  29B0000 = 43712512)
    12. Multiply by 4096 to get the size in bytes (example:  43712512 x 4096 = 179046449152)
    13. Divide by 1000000 to get the size in millions of bytes (M) (example:  179046449152 / 1000000 = 179046.4)
    14. Round value up to whole integer (example:  179046.4 => 179047)
  2. Check the size of the non-configured unit that is intended to replace the LS (WRKDSKSTS or check in SST)
  3. If the non-configured unit equals, or is larger than, the value from step 1, you can migrate to the new unit
  4. If the non-configured unit is less than the value from step 1, continue with step 5
  5. Reduce the storage allocated on the LS and rebuild the free space map
    1. Mark the LS for no new allocations with command STRASPBAL TYPE(*ENDALC) UNIT(1)
    2. Start draining data off the LS using command STRASPBAL TYPE(*MOVDTA) TIMLMT(*NOMAX)
    3. Monitor status using command CHKASPBAL until the balance function is complete
    4. Set the system to compress job tables on next IPL using command CHGIPLA CPRJOBTBL(*NEXT)
    5. Perform a normal IPL (note:  job table compression can take a significant amount of time)
    6. Start another drain using command STRASPBAL TYPE(*MOVDTA) TIMLMT(*NOMAX)
    7. Monitor status using command CHKASPBAL until the balance function is complete
    8. Perform a second normal IPL to rebuild the free space map for unit 1
    9. Resume allocations for unit 1 using command STRASPBAL TYPE(*RSMALC) UNIT(1)
  6. Repeat step 1 to determine the new minimum size that can be used to replace the LS
  7. If the non-configured unit equals , or is larger than the new value from step 6, then you can migrate to the new unit
  8. If the non-configured unit is less than the value from step 6, you will need a larger drive to do the migration

Additional Information

Frequently asked questions (FAQ):
Q:  Will this procedure allow migrating to the minimum size LS (e.g. 70 GB)?
A:  Probably not.  Certain LIC structures like the Storage Management directories do not get moved by these steps and will limit the minimum size based on where these structures are located on disk.
Q:  Why do large LS units seem to allow only a very small reduction in LS size?
A:  STRASPBAL is limited to only moving data off the first 500 GB of a disk unit (7.3 and below), so units larger than 500 GB may have data beyond the 500 GB point which won't get moved.

Document Location


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Document Information

Modified date:
10 March 2020