Apple Xsan 2 (Third Edition) - Manual (Page 55)

Chapter 4 Managing SAN Storage 55
Adding LUNs to a Storage Pool
You can increase the size of a SAN volume by adding LUNs (RAID arrays or array slices)
to storage pools in the volume. If you’re expanding a volume that is based on a built-
in volume type, you add LUNs to affinity tags and Xsan Admin assigns those LUNs
to underlying storage pools for you, creating storage pools as needed, based on the
optimal number of LUNs per pool for the volume type (“Assigning LUNs to Affinity
Tags” on page 29). If you’re expanding a custom volume, you add LUNs directly to
storage pools.
Note: A storage pool can’t contain more than 32 LUNs, the total number of LUNs in
a volume can’t be greater than 512, and you can’t add LUNs to a storage pool that
contains only journal data or metadata.
Choosing Compatible LUNs
LUNs you add to an existing storage pool must be at least as large as the LUNs in the
pool. On the other hand, if a new LUN is larger than the other LUNs in the pool, its
extra capacity can’t be used. Always try to add LUNs that are identical or similar in
performance and capacity to the LUNs already in the storage pool. Mixing LUNs of
different sizes or speeds in the same storage pool wastes capacity and can degrade
performance.
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