Extended-Format Data Sets

When space for a striped extended-format data set is allocated, the system divides the primary amount among the volumes. If it does not divide evenly, the system rounds the amount up. For extended-format data sets, when the primary space on any volume is filled, the system allocates space on that volume. The amount is the secondary amount divided by the number of stripes. If the secondary amount cannot be divided evenly, the system rounds up the amount. Striped data sets are always allocated in tracks, irrespective of the unit of allocation specified on the define.

Data sets allocated in the extended-format achieve the added benefits of improved error detection when writing to DASD as well as the use of a more efficient and functionally complete interface to the I/O subsystem.

Table 1 shows how stripes for an extended-format sequential data set are different from stripes for an extended-format VSAM data set.

Table 1. Differences between stripes in sequential and VSAM data sets
Sequential Extended-Format Striped	VSAM Extended-Format Striped
The data set can have a maximum of 59 stripes.	The data set can have a maximum of 16 stripes.
Each stripe must reside on one volume and cannot be extended to another volume.	Each stripe can reside on one or more volumes. There is no advantage to increasing the number of stripes for VSAM to be able to acquire additional space. When extending a stripe to a new volume, the system derives the amount of the first space allocated according to the Additional Volume Amount in the data class. This space derived from the primary or secondary space. The default value is the primary space amount.
After the system fills a track, it writes the following blocks on a track in the next stripe.	After the system writes a control interval (CI), it writes the next CI on a track in the next stripe. A CI cannot span stripes.
You can use the BSAM and QSAM access methods.	You can use the VSAM access method.