(1) We use MPEX wherever possible to expand (or contract) a file - but I had one problem when we ran out of disk space during this operation. 

(2) We now only use KSAM/XL files.  
    - They use up far less disk space than KSAM/3000 files
    - There's only the one file to copy 
    - They are much more efficient than KSAM/3000 (since mpe isn't having to switch between Native and compatibility modes)  
    - You don't have to recover KSAM/XL files that were open when the system crashes  !!

(3) We use the ;REUSE option on files with a high volatility

(4) Variable length records aren't supported in KSAM/XL