先来看看几个XIV中最基本的概念：
Partitions
The fundamental building block of a logical volume is known as a partition.
Partition是1MB（1024KB），包括a primary copy 或者 secondary copy of data，每个Partition都对应一个单独的物理磁盘的某个区域，存储管理员不知道也无法控制一个Partition对应到哪个disk，它是由系统算法控制的。Secondary Copy是放在和Primary Copy不同的Module中的。
Logical volumes
1，每个Volume都是由N个1MB的Partition组成
2，Logical Volume的容量是17GB的倍数因为Volume会分布在系统所有的盘上
Storage pools
While the hardware resources within the BM XIV Storage System are virtualized in a global sense, the available capacity in the system can be administratively portioned into separate and independent storage pools.
Essentially, storage pools function as a means to effectively manage a related group of similarly provisioned logical volumes and their snapshots.
Storage Pools are Logical
–Allocates hardware resources
–Same performance for all storage pools
–Volumes can be moved between Storage Pools
–Volumes and their clones moved together
–No data movement involved… immediate results
Storage Pools control the storage resources
–Use for specific applications or departments
–Physical and Virtual storage used by volumes
–Limits physical space for clones
–Can be resized as needed… depending on available resources
下图是Storage Pool和Logical Volume的关系
Distribution table
distribution table在系统启动的时候创建，包含了Primary和Secondary Partition的映射，还有Module和相应Disk的mapping。当硬件改动时，会创建新的distribution table然后deliver到每个Module上。每个Module都包含了一份distribution table。
XIV Running state
当两份Copy（Primary Copy和Secondary Copy）同时都在时，系统就是在Full Redundancy 状态。
When the full redundancy of data is compromised due to a disk or module failure, the XIV Storage System immediately identifies the non-redundant partitions and begins the rebuild process. The rebuild process consists of the following activities:
--Creates a new target data distribution
--Makes a copy of the non-redundant partitions and writes them according to the new target distribution. This process is known as rebuilding.
--Simultaneously begins to redistribute the redundant data according to the new target data distribution. This process is known as redistributing.
Important: After an XIV Storage System component failure, rebuild and redistribution begin immediately and at the same time.