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What to know before you create a LUN

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Why actual LUN sizes slightly vary

You should be aware of the following regarding the size of your LUNs.

  • When you create a LUN , the actual size of the LUN might vary slightly based on the OS type of the LUN. The LUN OS type cannot be modified after the LUN is created.

  • If you create a LUN at the max LUN size, be aware that the actual size of the LUN might be slightly less. ONTAP rounds down the limit to be slightly less.

  • The metadata for each LUN requires approximately 64 KB of space in the containing aggregate. When you create a LUN, you must ensure that the containing aggregate has enough space for the LUN's metadata. If the aggregate does not contain enough space for the LUN's metadata, some hosts might not be able to access the LUN.

Guidelines for assigning LUN IDs

Typically, the default LUN ID begins with 0 and is assigned in increments of 1 for each additional mapped LUN. The host associates the LUN ID with the location and path name of the LUN. The range of valid LUN ID numbers depends on the host. For detailed information, see the documentation provided with your Host Utilities.

Guidelines for mapping LUNs to igroups

  • You can map a LUN only once to an igroup.

  • As a best practice, you should map a LUN to only one specific initiator through the igroup.

  • You can add a single initiator to multiple igroups, but the initiator can be mapped to only one LUN.

  • You cannot use the same LUN ID for two LUNs mapped to the same igroup.

  • You should use the same protocol type for igroups and port sets.