Accusys ExaSAN SW-08 - Manual (Page 55)

6. Xsan
User Guide Page 6-4
6.4.3 Volumes
Storage pools are combined to create the volumes that users see. From the user’s perspective, the Xsan
volume looks and behaves like a large local disk, except that:
1. the size of the volume can grow as you add underlying arrays or new storage pools
2. multiple users on the SAN can access files on the volume at the same time
In the illustration in Section 6.3, two storage pools (a metadata pool and a data pool) are combined to
create a single shared Xsan volume. You use Xsan Admin to create volumes and mount them on client
computers.
The following screenshot shows how LUNs, storage pools, and volumes look as you organize them in
Xsan Admin. This example shows a SAN with a single shared volume. There are two storage pools.
6.5 How Xsan Uses Available Storage
Xsan stores user files and file system data on storage pools, and stripes data across the LUNs in a storage
pool for better performance.
6.5.1 Metadata and Journal Data
Xsan records information about the files in an Xsan volume using metadata files and file system journals.
File system metadata includes information such as which specific parts of which disks are used to store a
file and whether the file is being accessed. The journal data includes a record of file system transactions
that help ensure the integrity of files in the event of a failure.
These files are managed by the Xsan metadata controller but are stored on ExaSAN storage, not on the
controller itself. Metadata and journal data are stored on the first storage pool you add to a volume.