If you are planning to use the Copy Export function, plan for enough physical volumes for the Copy Export function and enough storage cells for the volumes in the library destined for Copy Export or in the Copy Export state. The Copy Export function defaults to a maximum of 2,000 physical volumes in the Copy Export state. This number includes offsite volumes, the volumes that are still in the physical library that are in the Copy Export state, and the empty, filling, and full physical volumes that eventually are set to the Copy Export state. 

The default value can be adjusted through the MI (use the Copy Export Settings window) to a maximum value of 10,000. After your Copy Export operations reach a steady state, approximately the same number of physical volumes is being returned to the library for reclamation because there are those being sent offsite as new members of the Copy Export set of volumes. 

## 4.4.5 Data compression 

Starting with R4.1.2, the following options are available for TS7700 data compression: 

GLYPH<SM590000> FICON compression: Same compression method that was available for previous releases and is embedded on the Ficon adapter. 

GLYPH<SM590000> LZ4 compression: Compression algorithm that prioritizes processing speed. 

GLYPH<SM590000> ZSTD compression: As with LZ4, it is a lossless algorithm but, unlike the latter, it aims for the best possible compression ratio, which might come with a speed tradeoff. 

No special feature code is needed for these options to be available, but all clusters in the Grid must run R4.1.2 or later (the presence of lower levels of code in the grid will prevent the use of this feature). 

Different virtual volumes in the same grid can use different compression algorithms, depending on Data Class construct assignment (which contain the selected algorithm information). This feature implies this option is a grid-scope setting. The option to be selected depends on the wanted compression ratio/speed level. 

Only virtual volumes that are written from BOT can go through LZ4/ZSTD processing (if its associated Data Class is configured for that compression method). Previously written data in virtual volumes keep the initially applied compression method, even if Data Class parameters are changed. A method is not available to convert old data to the new compression algorithms. 

Note:  The uncompressed data size that can be written to a single virtual volume includes a “logical” limit of 68 GB for channel byte counters tracking the amount of written data. This limit can be surpassed when compression rates are used that are equal or higher than 2.7:1 (with FICON traditional compression or the new enhanced algorithms) against volumes that are assigned to Data Classes configured for 25,000 MiB volume sizes (after compression). 

Considering that circumstance, Data Classes can now be configured to decide how to handle that event by using the new attribute 3490 Counters Handling with the following available options: 

GLYPH<SM590000> Surface EOT: Set this option to surface EOT (End Of Tape) when channel bytes written reaches maximum channel byte counter (68 GB). 

GLYPH<SM590000> Wrap Supported: Set this option to allow channel bytes written to exceed maximum counter-value and present the counter overflow unit attention to the attached LPAR, which then can collect and reset the counters in the TS7700 by using the RBL (X'24') command. 

