Instant Snapshot with nonpartitioned indexes

You can substantially improve the performance of copying storage-group-defined nonpartitioned indexes by using the XBM product’s Instant Snapshot technology. Instant Snapshots are hardware-based copies that do not require the I/O that is needed to make a software-based copy.

The following considerations apply when using the SIXSNAP option.

Timeout considerations

Using Instant Snapshot can improve the performance of the reorganization, but can also cause applications to time out. For example, a timeout might occur when REORG PLUS copies a large number of nonpartitioned indexes or a multi-data-set index that contains a large number of pieces.

The size of the data sets to be copied does not matter. The number of data sets affects timeouts because the Instant Snapshot requests (one per index or piece) are serial. If these requests take longer than the standard SQL timeout value (IRLMRWT) that is defined in DSNZPARMs for your site, the application times out with SQL code -911.

To calculate the time required to perform the Instant Snapshot, allow approximately 8 to 10 seconds (depending on the hardware and version of the microcode) per index or piece. If this value is less than the IRLMRWT value, the application should not time out.

A timeout can also occur when REORG PLUS begins Instant Snapshot processing but discovers that the required hardware is not available.

Hardware vendor considerations

The results of using SIXSNAP can vary depending on the hardware vendor that you are using for the DASD devices.

• SMS controlled

  If the target data set (snapped copy) is SMS-controlled and uses fewer volumes than the source data set, the additional volumes remain candidate volumes with a volume name of * (asterisk).

• EMC

  Regardless of the order in which you pass the storage group volumes, EMC sorts the volumes from the one with the greatest amount of available space to the one with the least amount of available space, and allocates them in that order.

• STK

  STK allocates the volumes in the order that you pass them. However, if the first volume in the list does not contain enough room for the primary allocation, the allocation fails. If you specify SIXSNAP YES, the reorganization fails if this volume allocation fails. If you specify SIXSNAP AUTO, REORG PLUS changes it to SIXSNAP NO and performs the software-based copy. Therefore, BMC recommends that you specify SIXSNAP AUTO instead of YES.