420 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
To implement offload throttle, you can use the mkthrottle command with -type offload 
parameter, or GUI, as shown in Figure 10-11.
Figure 10-11   Setting offload throttle
10.4  Data Reduction Pools
Data Reduction Pools (DRP) increase infrastructure capacity use by using new efficiency 
functions and reducing storage costs. The pools enable you to automatically de-allocate and 
reclaim capacity of thin-provisioned volumes that contain deleted data and for the first time, 
enable this reclaimed capacity to be reused by other volumes. Data reduction pools support 
volume compression. Also, they support deduplication that can be configured with 
thin-provisioned and compressed volumes.
10.4.1  Introduction to DRPs
At its core, a DRP uses a Log Structured Array (LSA) to allocate capacity. A log structured 
array allows a tree-like directory to be used to define the physical placement of data blocks 
independent of size and logical location. Each logical block device has a range of Logical 
Block Addresses (LBAs), starting from 0 and ending with the block address that fills the 
capacity. 
When written, an LSA allows you to allocate data sequentially and provide a directory that 
provides a lookup to match LBA with physical address within the array. Therefore, the volume 
you create from the pool to present to a host application consists of a directory that stores the 
allocation of blocks within the capacity of the pool.
In data reduction pools, the maintenance of the metadata results in I/O amplification. I/O 
amplification occurs when a single host-generated read or write I/O results in more than one 
back-end storage I/O requests because of advanced functions. A read request from the host 
results in two I/O requests, a directory lookup, and a data read. A write request from the host 
results in three I/O requests, a directory lookup, a directory update, and a data write. 
DRP technology allows you to create five types of volumes:
/SM590000Fully allocated
This type provides no storage efficiency.
/SM590000Thin-provisioned
This type provides some storage efficiency but no compression or deduplication. Volume 
capacity is allocated on demand as storage is first written.
Note: This book provides only an overview of DRP aspects. For more information, see 
Introduction and Implementation of Data Reduction Pools and Deduplication, SG24-8430.