About RANKs and LUNs in Storage Utility

With Storage Utility you bind disks into a group. This group is a logical unit recognized by the Windows operating system, the media file system, and other software. A logical unit is called a LUN, which stands for Logical Unit Number. You can combine one or more LUNs into a group called a RANK.

Storage Utility for K2 SAN uses RANK to define the group. In contrast, Storage Utility for stand-alone K2 storage uses LUN to define the group.

The distinction between LUN and RANK is necessary because the maximum disk size recognized by some older Windows operating systems is relatively low, and in a K2 SAN with large capacity disks, a group of disks can exceed this maximum size. To solve the problem, Storage Utility binds disks as smaller size LUNs which can be recognized by the Windows operating system as a logical disk. Then multiple LUNs are combined into a RANK, as required to support the K2 SAN.

K2 software version 9.0 and higher takes advantage of recent Windows operating systems that have a much higher maximum disk size and are able to accommodate LUNs with large capacity disks. So for systems new with K2 software version 9.0 and higher, all binding of disks must be one LUN per RANK. However, for the purpose of expanding existing storage pools, binding multiple LUNs per RANK is still available.

In Storage Utility, there is no operational difference between what is currently labeled a RANK and what was previously labeled a LUN. The tasks you perform are identical. However, Storage Utility reports the number of LUNs in each RANK, which is useful information if you need to view disks from Windows operating system administrative tools.

In systems on which Storage Utility bound disks to fit the limitations of the older Windows operating systems, LUNs per RANK are as follows:
Drives RAID 5 RAID 6
500 GB 7.2K 2 LUNs/RANK 1 LUN/RANK
600 GB 15K 4 LUNs/RANK 4 LUNs/RANK
1 TB 7.2K 4 LUNS/RANK 2 LUNS/RANK

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