17 Top VSAM Tuning Tips

Tuning VSAM files tips are necessary to improve file performance. Data with Index faster in response, so these are useful to apply in the mainframe projects.

VISAM Tuning Tips

Always use efficient Data and Index CI sizes.
Assuming your record size permits, 4K/8K works best for the Data CI size of
CICS online files. The Index CI should be large enough to hold all of the index entries for a DATA. VSAM is clearly explained in the express edition.
For large keys that do not compress well, this could be 8K/16K. Too small an Index CI may result in unnecessary CA splits.
The Index CI should be also large enough so that Index Levels is no more than 2 if possible. You can make it too big but 2K is often too small.
Always define your VSAM clusters with the SPEED parameter.
CI and CA Splits can greatly reduce CICS response time.
Code CI and CA Freespace very carefully and monitor regularly.
REORG of files does NOT fix splitting problems. It just covers the problem up for a short period of time.
Allocate better FREESPACE.
Never use SHROPT 4 if at all possible.
Do not use ERASE ever.
Do not use WRITECHECK ever.
Do not use IMBED or REPLICATE, they are no longer supported and they waste DASD space.
Optimize VSAM performance for both random and sequential processing by always specifying the appropriate number of NSR or LSR buffers.
Remove Catalog Orphans from the Catalog.
Make all ESDS files use the SPANNED parameter. (ref: IBM)