Apple Xsan 2 (Third Edition) - Manual (Page 63)

Chapter 4 Managing SAN Storage 63
Changing Storage Pool Settings
The SAN Setup assistant chooses storage pool settings based on the type of volume
you create. To specify storage pool settings yourself, choose an affinity tag or storage
pool on the Configure Volume Affinities pane of the SAN Setup assistant when you
create the volume and click the Settings button below the list.
The best way to set up a SAN is to plan its organization carefully before you set it up,
including settings for the storage pools that make up its volumes. To change storage
pool settings for an existing volume, you must destroy and recreate the volume.
Changing the Exclusivity of an Affinity Tag
The “Use for” affinity tag setting specifies the type of data that can be stored on a
storage pool with that tag. You can choose to allow metadata only, user data only, or
both. You make this choice when you create the volume, and can’t change it without
recreating the volume.
If you chose to allow user data only, you can further specify whether the data has to
have the matching affinity. If the data must have the matching affinity, the tag is called
“exclusive,” and data without the affinity isn’t allowed. You can change this setting as
needed.
To change the exclusivity of an affinity tag:
1 In Xsan Admin, select the storage pool in the Volumes pane and choose Edit Affinity
Settings from the Action (gear) pop-up menu.
2 Click the checkbox to select or deselect “Only data with affinity.”
If the checkbox is disabled, this is the last affinity tag in the volume that isn’t exclusive.
A volume must contain at least one affinity tag that isn’t exclusive. In other words, the
volume must contain at least one affinity tag that accepts user data without an affinity.
Setting the Storage Pool Stripe Breadth
Xsan uses both the storage pool stripe breadth and the volume block allocation size
to decide how to write data to a volume. For most SANs, the default values for storage
pool stripe breadth and volume block allocation size result in good performance.
However, in some cases you might be able to improve read and write performance by
adjusting these values to suit a specific application.
The stripe breadth must be set when the volume is created; it can’t be changed for an
existing volume.
To set a storage pool’s stripe breadth:
Click the Settings button below the Affinity Tag list on the Configure Volume Affinities
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pane of the setup assistant when you create the volume.