Virtual Devices Will Not Vary Online

Several problems can occur when you try to vary the Virtual Devices online. Two of the most common are as follows:

If the Virtual Devices were not properly defined with HCD, the following message is issued:
```
IEE313I nnn             UNIT REF. INVALID
```
Review the HCD definitions and correct the errors.

Also verify within IPCS. From option 6, issue the following command:
```
SETD ACTIVE
```
```
LISTUCB ucb
```
where ucb is the device address you are investigating.

In the UCBXPX at offset +0C, you find the SIDA and SCHNO fields. If the values in these fields are 0000s, then CA Vtape successfully allocates this address. If these fields contain anything other than 0000s, then you need to define another range.

CA Vtape uses this safety mechanism to ensure that no physical devices are associated with the UCB. After CA Vtape uses these devices, other resources can use the UCB only after the next IPL.
If you try to vary the Virtual Devices online without the SVTS STC active, you get the following message:
```
IEE025I UNIT nnn HAS NO LOGICAL PATHS
```

If you do not define enough Virtual Volumes, CA Vtape displays the SDSF SYSLOG Scratch Shortage message, as shown in the following example:

Screen shot example of the the SDSF SYSLOG Scratch Shortage message.