Migration Considerations for the 3390 Model 9

The z/VM® support of 3390 Model 9 will not affect migration, but there are data migration considerations if you plan to move data from other devices to a 3390 Model 9.

The 3390 Model 9 is formatted as a CKD device and is supported for formatting by ICKDSF and the CPFMTXA utility. The allocation map format on a 3390 Model 9 device will be an extent-based allocation map as opposed to the cylinder-based allocation map currently used for existing CKD DASD. This is because the existing 4K cylinder-based allocation record is not large enough to account for the number of cylinders on a 3390 Model 9 device.

Because the DDR command is capable of doing a straight copy from an existing 3390 device to a 3390 Model 9 device, this may result in a Model 9 device having a cylinder-based allocation map record. The 3390 Model 9 device will still be usable by z/VM, but because of the limitation of the cylinder-based allocation map record, only the first 4K cylinders of the device will be capable of being used.

The reverse situation is also possible where a 3390 Model 1, 2 or 3 device could have an extent-based allocation map. This, however, will not be allowed by CP. If a 3390 contains an extent-based allocation map and an operator attempts to attach this 3390 Model 1, 2 or 3 as a CP volume, a warning message will be issued.

If either type of data movement is performed, the output disk should be reallocated using the ICKDSF CPVOLUME ALLOCATE command if the device is intended to be used as a CP volume. ICKDSF will convert a cylinder-based allocation map record on a 3390 Model 9 device into the extent-based allocation record that is necessary to use the entire device. An extent-based allocation record found on a 3390 model 1, 2 or 3 can also be converted by ICKDSF into a cylinder-based allocation map record.