While merging two stacks Stack A and Stack B and you want Stack A to take over the entire stack, it is always recommened to reset the other stack configuration. On Stack B execute "restore factory_default stacking" and then add the Serial number of these member to Stack A.
In a two-member stack with split-detection enabled, both the members of the stack remain active.
(WINNER STACK) #show stacking members
Member status: Active, Stack Id: 000b866a5ac04f7a47c4 Stack uptime: 19 minutes 57 seconds
Id Role MAC Address Priority State Model Serial
-- ---- ----------- -------- ----- ----- ------
0 * Primary 000b.866a.5ac0 Preset Active ArubaS3500-48P AW0000155
2 Secondary 000b.866a.7500 Preset Active ArubaS3500-24T AU0000229
Disable split-detection
(WINNER STACK) #show stack-profile stack-profile "default"
Parameter Value
MAC persistence timeout 15 Minutes Split Detection Disabled
Preset-profile:
Member-id Serial-number Role
0 AW0000155 Primary-capable
2 AU0000229 Primary-capable
In the case the stack is down or the stack interfaces go down, both units will act as independent Primary
(WINNER STACK) #show stacking members
Member status: Active, Stack Id: 000b866a5ac04f7a47c4
Stack uptime: 22 minutes 13 seconds
Id Role MAC Address Priority State Model Serial
-- ---- ----------- -------- ----- ----- ------
0 * Primary 000b.866a.5ac0 Preset Active ArubaS3500-48P AW0000155
2 Unknown 000b.866a.7500 Preset Away ArubaS3500-24T AU0000229
Output as shown on the member 2 console.
(WINNER STACK) #show stacking members
Member status: Active, Stack Id: 000b866a75004f7a4e44
Stack uptime: 22 minutes 29 seconds
Id Role MAC Address Priority State Model Serial
-- ---- ----------- -------- ----- ----- ------
0 Unknown 000b.866a.5ac0 Preset Away ArubaS3500-48P AW0000155
2 * Primary 000b.866a.7500 Preset Active ArubaS3500-24T AU0000229
Once the stack interface are back up the stack is re-formed as original stack
(WINNER STACK) #show stacking members
Member status: Active, Stack Id: 000b866a5ac04f7a47c4
Stack uptime: 26 minutes 6 seconds
Id Role MAC Address Priority State Model Serial
-- ---- ----------- -------- ----- ----- ------
0 * Primary 000b.866a.5ac0 Preset Active ArubaS3500-48P AW0000155
2 Secondary 000b.866a.7500 Preset Active ArubaS3500-24T AU0000229