Xsan: How to determine available capacity

Use the steps below to accurately detemine available capacity of an Xsan volume.

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Understanding capacity 

A volume may reach maximum capacity in two ways:

  1. Xsan creates inodes on demand rather than creating inodes when a volume is formatted. When there is no space left in the metadata storage pool to create inodes, and if there are no recycled inodes available, then the Xsan volume is considered to have reached maximum capacity.
  2. If the storage pools that are designated for data storage become full, the volume is considered to have reached maximum capacity.
     

Determining available space in the Metadata Storage

Calculate the metadata storage pool capacity in two ways:

  1. Observe the amount of available storage in the metadata storage pool

    In order to observe the amount of available space on storage pools designated as metadata storage, open Xsan Admin and select Volumes. Click the disclosure triangle next to the Volume you wish to inspect. Note the percent used bars next to the storage pools designated for metadata storage. (By default, the first storage pool in the list is the location for metadata storage.) 
     
  2. Observe how many inodes are waiting to be reused, following their associated file's deletion.

    In order to determine the amount of reusable inodes in a metadata storage pool, use the command-line utility df, in Terminal:

    sudo df -i /Volumes/YourVolumeName

    Note: Replace YourVolumeName with the name of the Xsan volume you wish to inspect.

Example output:

Filesystem   512-blocks    Used          Available     Capacity   iused    ifree     %iused   Mounted on
/dev/disk5   14651367936   8790820762    5860547174    60%        828334   552223    60%      /Volumes/MyVolume


This output indicates that 40% of the inodes on this Xsan volume are available for use. 
 

Determining available space in the Data Storage

In order to observe the amount of available space on storage pools designated as Data storage, open Xsan Admin and select Volumes. Click the disclosure triangle next to the Volume you wish to inspect. Note the percent used bars next to the storage pools designated for data storage.

A subset of storage pools may fill up faster than other storage pools. For example, a storage pool associated with an affinity may reach maximum capacity faster than another set of storage pools associated with another affinity. Storage pools that are not associated with an affinity may reach maximum capacity before storage pools that are associated with affinities. 

Adding Capacity:

If a storage pool designated for data storage has reached maximum capacity, data storage may be added to the volume by performing the following:

Xsan 1.4.2 or earlier:

  • Add LUNs to existing storage pools or create new storage pools.

Xsan 2.0 or later:

  • If an Xsan volume was created using a preset volume configuration, add LUNs to existing affinities or create new affinities.
  • If an Xsan volume was created using a custom volume configuration, add LUNs to existing storage pools or create new storage pools.
     

If a storage pool designated for metadata storage has reached maximum capacity, metadata storage can be freed by deleting files from the Xsan volume. Alternately, create a new storage pool and configure it to store metadata.

Utilities such as  df -h  or  df -H  may provide inaccurate available capacity statistics for an Xsan volume.

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