In-Memory databases are hosted entirely in memory in the Adaptive Server buffer cache, and do not require disk devices.
To create an in-memory database:
Create an in-memory storage cache.
Create one or more in-memory devices on the in-memory storage cache.
Create an in-memory database on an in-memory device.
A database cannot exist on more than one cache. However,
you can create more than one device on a cache that the database
can use. When you create a database on a cache you have the opportunity
to specify the devices that database uses. At this time, any devices
you specify must all reside on the same cache.