When using raw devices in Informix, what is a chunk?

Introduction / Context:
This question tests knowledge of Informix storage terminology. When a database uses raw devices instead of cooked filesystems, it allocates logical units of storage called chunks. Understanding chunks is fundamental for planning dbspaces, monitoring storage, and interpreting administrative commands.

Given Data / Assumptions:

The database uses raw devices for storage rather than regular files.

Chunks are configured as part of dbspaces.

Each chunk represents a specific, well defined portion of disk space.

The question asks for the correct definition of a chunk in this context.

Concept / Approach:
In Informix, a chunk is defined as a contiguous area of disk space allocated to the database, typically on a raw device. Chunks are grouped into dbspaces, which hold tables, indexes, and other objects. They are not memory regions or dynamic constructs that change size automatically. Contiguous allocation helps performance and simplifies addressing within the chunk.

Step-by-Step Solution:
1. Recall that chunks are disk level entities, not memory structures. 2. Recognize that the term contiguous refers to a continuous sequence of disk blocks, which is how chunks are normally allocated. 3. Evaluate option C, which matches the idea of a contiguous region of disk on a raw device used by the database. 4. Option A suggests automatic size changes, which is not the basic definition of a chunk. 5. Options B and D incorrectly tie chunks to shared memory or in memory tables rather than disk storage.

Verification / Alternative check:
Informix manuals describe chunks as contiguous units of storage within dbspaces. Utilities such as onstat and oncheck report chunk numbers and their associated raw devices, further confirming the definition.

Why Other Options Are Wrong:
Dynamic changes in size may be supported at higher levels but do not define what a chunk is.
Shared memory locations are part of buffer pools and caches, not chunks.
In memory tables are a separate concept and not represented by the word chunk in Informix storage terminology.

Common Pitfalls:
A common confusion is mixing the idea of a chunk with higher level logical units like tables or buffer pools. Keeping in mind that chunks are raw disk allocations helps when sizing and placing dbspaces for performance and reliability.

Final Answer:
A chunk is a contiguous unit of disk space on a raw device used by the Informix database.