Check with your ADABAS colleagues which disk access method is used by ADABAS? is it VSAM, BDAM,... or PIOCS. PIOCS is used by IDMS. IDMS doesn't rely on IBM standard BDAM/VSAM macros. The physical reads and writes are executed in IDMS code at the lowest level coded in assembler. So check how ADABAS performs reads/writes. This would help to evaluate if IDMS is maybe exposed to the same performance problem with model 54 disks.