Veritas Storage Foundation 5.1 SP1: Storage and Availability Management for Oracle (5900-1504, April 2011)

system increases over time, additional space in the form of new disks must be
added.
To increase space, you could perform a volume relayout using the command.
However, changing a large volume, for example, from a four-way striped volume
to six-way striped volume involves moving old block information into temporary
space and writing those blocks from the temporary space to a new volume, which
would require an extended amount of time. To solve this problem, SFDB tools
provide the Extent Balanced File System or EBFS .
An Extent Balanced File System is created on a multi-volume file system where
individual volumes are not striped over individual disks. For data-availability,
these individual volumes can be mirrored. The file system on the EBFS has a
special placement policy called a balance policy. When the balance policy is applied,
all the files are divided in vxrelayout to small "chunks" and the chunks are laid
out on volumes so that adjacent chunks are on different volumes. The default
chunk size is 1MB and can be modified. Since every file contains chunks on all
available volumes, it is important that individual volumes that make up the EBFS
and volume set be of same size and same access properties.
Setting up the file system in this way provides the same benefit as striping your
volumes.
Note: You cannot convert an existing file system to an EBFS file system.
Extent balancing file system
You can define allocation policies with a balance allocation order and "chunk"
size to files or a file system, known as extent balancing. The chunk size is the
maximum size of any extent that files or a file system with this assigned policy
can have. The chunk size can only be specified for allocation policies with a balance
allocation order.
An extent balancing policy specifies the balance allocation order and a non-zero
chunk size. The balance allocation order distributes allocations randomly across
the volumes specified in the policy and limits each allocation to a maximum size
equal to the specified chunk size.
Extent balancing extends the behavior of policy enforcement by rebalancing
extent allocations such that each volume in the policy is as equally used as possible.
Policy enforcement handles the following cases:
■ New volumes are added to the policy, and the extents associated with a file
need rebalancing across all volumes, including the new ones.
261Configuring and administering SmartTier
Extent balancing in a database environment