Replacing a mirrored unit

A unit selected to replace the failed mirrored unit must satisfy all of the mirrored protection configuration rules and restrictions when it is paired with the remaining unit in the mirrored pair.

You can replace mirrored units by using the Replace Disk Unit option in either dedicated service tools (DST) or system service tools (SST). To do this, you need to have a spare storage unit that can be paired with the mirrored unit of the storage unit that is being replaced. The storage unit being replaced can have a status of active or suspended. However, one of the storage units in the pair must be suspended. The results of the replace operation is different for each status. Replacing a suspended storage unit causes that storage unit to go to a status of resuming after the replace operation. Replacing an active unit causes data in the auxiliary storage pool (ASP) to be lost, so you must first delete the data in ASP (using the DST Delete ASP Data option). The storage unit being replaced can also be missing or not missing. To replace a unit with a status of resuming, you must suspend it. If the status of unit 1 is unknown, replace operations are not allowed until the status of the mirrored units for unit 1 is known. The unit selected to replace another mirrored unit must satisfy all of the mirrored protection configuration rules and restrictions when it is paired with the remaining unit in the mirrored pair.

If a storage unit fails, and if the same storage unit that failed has been repaired, it is not necessary to replace it. The failed disk should have a status of suspended and can be resumed after the repair is complete.

If the storage unit that is being replaced is active, it can only be replaced at DST before the initial program load (IPL) to the IBM i licensed program. It should never be necessary to replace an active unit unless both units of the mirrored pair have failed. If this situation does occur, the service representative should first try to recover the data from the failed units using the Save Disk Unit Data option on the Work with Disk Unit Recovery display. When an active unit is replaced, the last good copy of the data has been lost. The data in the ASP that contains the unit being replaced must be deleted using the DST Delete ASP Data option before an active unit is allowed to be replaced.

Replacing unit 1 requires special handling. If the system ASP has mirrored protection, one of the units in the mirrored pair for unit 1 is selected as the IPL device. It is the only unit that is used until the system performs an IPL to the IBM i licensed program. Until then, it cannot be replaced or even suspended. However, its mirrored unit can be both suspended and replaced. After the IPL to the IBM i licensed program, the IPL device can be suspended and then replaced.

Replacing a unit might cause the level of protection for a mirrored pair to change. If a lower level of protection results from a replacement operation, it shows a warning display. At certain times, especially when missing units are involved in the replace operation, the system might not be able to accurately calculate the level of protection and the same warning display is shown.

To replace a disk unit by using SST, follow these steps:

Type: STRSST
From the System Service Tools (SST) menu, follow these steps:
1. Select option 3 (Work with disk units).
2. Select option 3 (Work with disk unit recovery) on the Work with Disk Unit display.

Select option 1 (Replace configured unit) on the Work with Disk Unit Recovery display and press the Enter key.

The Select Configured Unit to Replace display is shown.

                      Select Configured Unit to Replace

   Type option, press Enter.   
1=Select
                         Serial
Resource OPT  Unit  ASP  Number      Type  Model  Name       Status
  _            1     1   00-0163477  6602   030   DD019      Suspended
  1            2     1   00-17900    6602   030   DD002      Suspended

Type a 1 in the Option column on the Select Configured Unit to Replace display and press the Enter key.

                       Select Replacement Unit
                    Serial
Resource Unit  ASP  Number      Type  Model  Name       Status
    2     1         00-17900    6602   030   DD002      Suspended 

Type option, press Enter.   1=Select

                Serial
Resource Option Number      Type  Model  Name       Status
   _            00-0330477  6602   030   DD005      Non-configured
   1            00-0323200  6602   030   DD033      Non-configured

Type a 1 in the Option column on the Select Replacement Unit display and press the Enter key.

                       Confirm Replace of Configured Unit

   This screen allows the confirmation of the configured unit to be replaced
with the selected replacement unit.  Press Enter to confirm your choices for
Replace Press F12 to return to change your choices.   The configured unit
being replaced is:
                   Serial
Resource Unit ASP  Number      Type  Model  Name      Status
           2    1  00-17900    6602   030   DD002     Suspended

The replacement unit will be:
                   Serial
Resource Unit ASP  Number      Type  Model  Name      Status
           2    1  00-0323200  6602   030   DD033     Resuming

Press Enter to confirm.
The replacement function runs for several minutes. Wait until the replacement function completes.