Veritas™ File System 5.0.1 Administrator's Guide

Load balancing

An allocation policy with the balance allocation order can be defined and assigned

to files that must have their allocations distributed at random between a set of

specified volumes. Each extent associated with these files are limited to a maximum

size that is defined as the required chunk size in the allocation policy. The

distribution of the extents is mostly equal if none of the volumes are full or

disabled.

Load balancing allocation policies can be assigned to individual files or for all files

in the file system. Although intended for balancing data extents across volumes,

a load balancing policy can be assigned as a metadata policy if desired, without

any restrictions.

Note: If a file has both a fixed extent size set and an allocation policy for load

balancing, certain behavior can be expected. If the chunk size in the allocation

policy is greater than the fixed extent size, all extents for the file are limited by

the chunk size. For example, if the chunk size is 16 MB and the fixed extent size

is 3 MB, then the largest extent that satisfies both the conditions is 15 MB. If the

fixed extent size is larger than the chunk size, all extents are limited to the fixed

extent size. For example, if the chunk size is 2 MB and the fixed extent size is 3

MB, then all extents for the file are limited to 3 MB.

Defining and assigning a load balancing allocation policy

The following example defines a load balancing policy and assigns the policy to

the file, /mnt/file.db.

To define and assign the policy

Define the policy by specifying the -o balance and -c options:

# fsapadm define -o balance -c 2m /mnt loadbal vol1 vol2 vol3 vol4

Assign the policy:

# fsapadm assign /mnt/filedb loadbal meta

Rebalancing extents

Extents can be rebalanced by strictly enforcing the allocation policy. Rebalancing

is generally required when volumes are added or removed from the policy or when

the chunk size is modified. When volumes are removed from the volume set, any

Multi-volume file systems

Load balancing

138