StorNext has multiple allocation strategies which can be set at the file system level. These strategies control where a new file’s first blocks will be allocated. Affinities modify this behavior in two ways:
A file with an affinity is usually allocated on a stripe group with matching affinity, unless the affinity is a preferred affinity.
A stripe group with an affinity and the exclusive attribute is used only for allocations by files with matching affinity.
Once a file has been created, StorNext attempts to keep all of its data on the same stripe group. If there is no more space on that stripe group, data may be allocated from another stripe group. The exception to this is when InodeStripeWidth is set to a non-zero value. For additional information about InodeStripeWidth, refer to the snfs_confg(5) man page.
If the file has an affinity, only stripe groups with that affinity are considered. If all stripe groups with that affinity are full, new space may not be allocated for the file, even if other stripe groups are available. The AffinityPreference parameter can be used to allow file allocations for an affinity that would result in ENOSPAC to allocate on other stripe groups (using an affinity of 0). See the snfs_config(5) man page for details.
When a file system with two affinities is to be managed by the Storage Manager, the GUI forces those affinities to be named tier1 and tier2. This will cause an issue if a site has an existing unmanaged file system with two affinities with different names and wants to change that file system to be managed. There is a process for converting a file system so it can be managed but it is non-trivial and time consuming. Please contact Quantum Support if this is desired.
Note: The restriction is in the StorNext GUI because of a current system limitation where affinity names must match between one managed file system and another. If a site was upgraded from a pre-4.0 version to post-4.0, the affinity names get passed along during the upgrade. For example, if prior to StorNext 4.0 the affinity names were aff1 and aff2, the GUI would restrict any new file systems to have those affinity names as opposed to tier1 and tier2.
