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When is a LUN Truly Free?

Level 9

As much as I enjoy waxing existential over what is means to be truly free, this discussion is limited to what it means for a LUN to be truly free in Storage Manager. Storage Manager is able to monitor storage environments containing devices from different vendors. These devices can define free LUNs differently. To understand what it means for a LUN to be truly free, we must  understand the definition of a free LUN and the definition of a Replication Target LUN.

Definition of a Free LUN

Generally free LUNs are created but not assigned to a host. These LUNs are potential candidates for reclaiming space on a storage array. Because free LUNs are not assigned to a host, they do not have an HBA mapping.

Definition of a Replication Target LUN

Replication target LUNs are used to replicate a source LUN so the information on the Replication Target LUN is redundant. These Replication Target LUNs are associated with their source LUN, and the Replication Target LUNs are not presented to a Host. Unlike the space on a free LUN, the space of a Replication Target LUN is used and cannot be reclaimed by a storage array. Replication Target LUNs do not have HBA mappings since there is no association with a host.

Example: LSI and HP EVA

According to LSI and HP EVA arrays, a free LUN is any LUN without an HBA mapping.So for these arrays, Storage Manager lists the Replication Target LUNs as "Free LUNs".

Navigate to the Free LUNs report from the left-hand navigation pane > SAN Groups > YourArrayName > Storage tab. An example is illustrated below.

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But as we saw in the definition of a Replication Target LUN, these LUNs are not truly free. However, if a meaningful naming convention is employed, and the names are adequately descriptive, then the replication LUNs can be identified within the Storage Manager reports. For example, use names such as <LUNName>_replication for your Replication Target LUNs.

1 Comment
Level 15

Interesting!

About the Author
I joined the SolarWinds ID team because want to use my skills and abilities towards a common goal, and I want know my contributions matter. I want to see the results of my efforts and work toward building something bigger than what I can accomplish on my own. I believe in the mystery of a can-do attitude, I am excited about new opportunities and knowledge, and I am glad to be part of the SolarWinds team. Before joining SolarWinds, I obtained a Masters and Bachelors degrees in Computer Science and spent 5 years with the IBM Tivoli ID team. I was trained as a technical writer to better fulfill my responsibilities in providing tools support to the ID team. In addition to these responsibilities, I lead a work group designed to organize efforts to use Web Analytics and statistics to drive and validate documentation improvement efforts. I transitioned to the Lead UI developer for a Transparent Development project and spent time learning and implementing social media strategies to improve user experience.