To determine the number of drives to set, consider MB/GB written to a pool, compute MiBps, compute maximum and average, and the number of premigration drives per pool. Base the number of drives by using 50 - 70 MBps per drive for models up to the TS1140, approximately 100 MBps for a TS1140, and approximately 140 MBps for a TS1150. These values are different from the native data rate because of the resources that are used by a TS7700 (for example, database updates and logical volume selection for premigration). 

## Avoiding Copy Export during heavy production periods 

Because a Copy Export operation requires each physical volume to be exported to be mounted, the best approach is to run the operation during a slower workload time. 

## 12.8.3 Number of back-end cartridges 

The number of needed back-end cartridges is determined not only by the amount of data that is stored on the cartridges. The following parameters also can influence the number of cartridges you need: 

GLYPH<SM590000> Reclaim value 

GLYPH<SM590000> Number of physical pools and pool properties 

GLYPH<SM590000> Delete Expire setting 

To monitor your situation and the trend of the cartridge usage, several possibilities are available, which are described next. 

## 12.8.4 Tuning of the usage of Back-end cartridges with VEHSTATS 

Several possibilities are available to influence the number of used backend cartridges. 

## Reclaim value 

As explained in the “Defining reclamation settings in a TS7700T” on page 544 back-end cartridge section, you can change the reclaim value to gain more empty cartridges. The lower the percentage of the reclaim value, the more cartridges are needed. The higher this value is, the more valid data needs to be transferred and physical tape drives are required. 

To find a good balance, review the active data distribution. At times, it is sufficient to change to a slightly higher reclaim value. 

## Amount of physical pool and pool properties 

For each physical pool, two empty cartridges often are kept inside the pool. Especially for smaller capacity configurations with large capacity cartridges such as JD media, larger number of cartridges is needed even if you do not want extra capacity. 

In addition, the pool properties should be reviewed. No borrow/Keep  has a negative influence. 

## Amount of physical pool and pool properties 

The delete expire value in the scratch categories defines how long a logical volume and the data on it is still be treated as valid data. For more information about delete expire, see 3.3.8, “Logical Volume Delete Expire Processing ve rsus previous implementations” on page 123. 

Note:  A short delete expire value might reduce your cartridge usage, but a short value does not enable you to rescue any unintentional deleted data. We suggest not to use a value below 5 days. A best practice is to use 7 days. 

