## 10.3 Expire Hold and scratch processing considerations 

This section describes the interaction between SCRATCH processing and the Expire Hold setting for scratch categories on the TS7700. For more information about the Expire and Expire Hold options for a category and the conditions that must be met for a volume that is assigned to the category to be delete-expired, see “Defining scratch categories” on page 553. 

When Expire Hold is set for a scratch category, it can heavily affect scratch volume availability. Consider the following cases: 

GLYPH<SM590000> Expire Hold option is enabled and the TS7700 is low on scratch volumes 

GLYPH<SM590000> Expire Hold option is enabled and Cache Utilization is beyond the wanted threshold in the TS7700D. 

## 10.3.1 Expire Hold and low on scratch volumes 

The Expire Hold option is used to ensure that a virtual volume that is sent to the SCRATCH pool cannot be reused or deleted before the grace period that is specified as the EXPIRE time passes. This fact can create a problem where the library might run out of available volumes to satisfy mount requests to write new data. 

If the EXPIRE time is set too long and not enough virtual volumes are released to keep a healthy level of SCRATCH volumes available, it might be necessary to reduce the EXPIRE time. 

However, this change affects only new volumes that are going into the SCRATCH pool. The existing volumes in the pool continue to be held until the original EXPIRE time passes. However, if Expire Hold is cleared, these volumes can then be added to the candidate list for SCRATCH mounts. Therefore, clearing the Expire Hold option immediately helps to alleviate the low on scratch condition, but it no longer protects data that inadvertently was sent to SCRATCH. The recovery of user data on volumes in the SCRATCH pool might no longer be certain. 

## 10.3.2 Expire Hold and cache utilization in a TS7700D 

When the Expire Hold option is enabled, the cache in a TS7700 is used up in part by holding data from virtual volumes that were sent to the SCRATCH pool. In addition to the risk of running out of virtual volumes to mount, a risk exists of running out of cache in a TS7700D when AUTOREMOVAL is not enabled. 

Again, consider EXPIRE time. If a TS7700D is consistently running high on cache usage, adjust this EXPIRE time. In this case, clearing the Expire Hold setting does not  immediately alleviate the high cache usage condition. The effect of disabling the Expire Hold from the cache perspective is to enable volumes in the SCRATCH pool to begin entering the candidate list for expire delete processing. 

A task runs in the library once per hour that processes some number of volumes from this list and reduces cache usage by deleting the expired volumes from cache. The number of volumes that are deleted per hour by default is 1000. 

The number of volumes that are moved to this candidate list is customizable (1000 - 2000), and is controlled by using the following command: 

LI REQ,composite-library,SETTING,DELEXP,COUNT,value 

