The different types of LUNs (Logical Unit Numbers) primarily describe how storage space is organized and presented to a server. These types can vary based on the storage system's capabilities and configuration. Based on the provided reference, and generally understood storage configurations, LUN types commonly include:
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Simple (or Basic) LUNs: This is the most straightforward type. A single LUN represents a contiguous block of storage on a single physical disk or RAID group. It offers no built-in redundancy or performance enhancement beyond what the underlying physical storage provides.
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Spanned LUNs: Also known as JBOD (Just a Bunch Of Disks). Spanned LUNs combine the storage space of multiple physical disks into a single logical volume. Data is written sequentially across the disks. If one disk fails, the entire LUN is lost. There is no fault tolerance.
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Striped LUNs: Striped LUNs, often implemented as RAID 0, distribute data evenly across multiple disks. This can significantly improve read and write performance because data is accessed in parallel. However, like spanned LUNs, there's no fault tolerance; if one disk fails, the entire LUN is compromised.
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Mirrored LUNs: Also known as RAID 1. Mirrored LUNs provide data redundancy by duplicating data across two or more disks. If one disk fails, the system can continue to operate using the mirror copy. This offers excellent data protection but reduces usable storage capacity (e.g., a two-disk mirror only provides the capacity of one disk).
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Striped with Parity LUNs: These LUNs, such as RAID 5 or RAID 6, combine striping with parity information. Parity is calculated data that can be used to reconstruct data on a failed disk. They offer a balance between performance and fault tolerance. RAID 5 uses a single parity disk, while RAID 6 uses two, providing higher fault tolerance. The performance of RAID 5/6 might suffer during write operations due to parity calculations.
Here's a table summarizing the LUN types:
| LUN Type | Description | Performance | Fault Tolerance |
|---|---|---|---|
| Simple (Basic) | Single contiguous storage block. | Moderate | None |
| Spanned (JBOD) | Combines multiple disks sequentially. | Moderate | None |
| Striped (RAID 0) | Data striped across multiple disks. | High | None |
| Mirrored (RAID 1) | Data duplicated across multiple disks. | Moderate | High |
| Striped with Parity (RAID 5/6) | Data striped with parity for redundancy. | Moderate to High | Moderate to High |
In Summary: The type of LUN chosen depends on the specific requirements of the application or system, balancing the need for performance, data protection, and storage efficiency. Understanding these different LUN types enables administrators to make informed decisions about storage configuration.
