HP XP P9500 Storage - Manual (Page 19)

Thin Provisioning concepts
Thin Provisioning is a volume management feature that allows storage managers and System
Administrators to efficiently plan and allocate storage to users or applications. It provides a platform
for the array to dynamically manage data without host involvement.
Thin Provisioning provides two important capabilities: thin provisioning of storage and enhanced
volume performance.
Thin Provisioning is more efficient than traditional provisioning strategies. It is implemented by
creating one or more Thin Provisioning pools (THP pools) of physical storage space using multiple
LDEVs. Then, you can establish virtual THP volumes (THP V-VOLs) and connect them to the individual
THP pools. In this way, capacity to support data can be randomly assigned on demand.
THP V-VOLs are of a user-specified logical size without any corresponding physical space. Actual
physical space (in 42-MB pool page units) is automatically assigned to a THP V-VOL from the
connected THP pool as that volume’s logical space is written to over time. A new volume does not
have any pool pages assigned to it. The pages are loaned out from its connected pool to that THP
volume until the volume is reformatted or deleted. At that point, all of that volume’s assigned pages
are returned to the pool’s free page list. This handling of logical and physical capacity is called
thin provisioning. In many cases, logical capacity will exceed physical capacity.
Thin Provisioning enhances volume performance. This is an automatic result of how THP V-VOLs
map capacity from individual THP pools. A pool is created using from one to 1024 LDEVs (pool
volumes) of physical space. Each pool volume is sectioned into 42-MB pages. Each page is
consecutively laid down on a number of RAID stripes from one pool volume. The pool’s 42-MB
pool pages are assigned on demand to any of the THP V-VOLs that are connected to that pool.
Other pages assigned over time to that THP V-VOL randomly originate from the next free page
from other pool volumes in that pool.
Setting up a Thin Provisioning environment requires a few extra steps. You still configure various
array groups to a desired RAID level, and then create one or more volumes (LDEVs) on each of
them (see
“Creating an LDEV” (page 51) ). But then you set up a Thin Provisioning environment by
creating one or more THP pools of physical storage space that are each a collection of some of
these internal LDEVs (THP pool volumes). This pool structure supports creation of Thin Provisioning
virtual volumes (THP V-VOLs), where 42-MB pages of data are randomly assigned on demand.
For detailed information, see “Configuring thin provisioning ” (page 62) .
When to use Thin Provisioning
Thin Provisioning is a best fit in an open-systems environment in the following scenarios:
•
Where the aggregation of storage pool capacity usage across many volumes demonstrates
largest performance optimization.
•
For stable environments and large consistently growing files or volumes.
•
If the application or file system does not write over areas that are not immediately needed.
•
Where the file system has a preference to write over deleted files.
Thin Provisioning advantages
With Thin Provisioning Without Thin Provisioning Advantages
You can logically allocate more capacity than
is physically installed. You can purchase less
capacity, reducing initial costs. You must purchase physical disk capacity for
expected future use. The unused capacity adds
costs for both the storage system and software
products. Reduces initial costs
Thin provisioning 19