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Calculation of the visible limit for both array LUNs and disks

Calculating the visible limit for a neighborhood requires that you consider the total number of disks and array LUNs combined.

Assume that in this neighborhood example there are two HA pairs and one stand-alone system, with disks connected to each system. The following table shows the maximum value used in this example for each limit.

Limit type Maximum allowed
Neighborhood maximum LUN limit (visible device limit) 1,200
Platform maximum assigned limit for the platform type (disks and array LUNs assigned combined) 500

The following table shows the calculations to determine whether the planned visible limit of array LUNs and disks in this neighborhood is within the supported limits. For simplicity, assume that there are no restrictions related to the storage arrays that present LUNs to the neighborhood members. (This table does not show the number of disks and LUNs assigned to each system.)

System Number of array LUNs seen Number of disks connected to it Total disks and array LUNs Within visible limits?
HA pair 1
vs-X 1,000 200 1,200 Yes
vs-Y 1,000 150 1,150 Yes
HA pair 2
vs-A 1,000 200 1,200 Yes
vs-B 1,000 350 1,350 No (The maximum visible device limit is 1,200.)
Stand-alone system
vs-standalone 1,000 100 1,100 Yes

All neighborhood members see all the same array LUNs. Therefore, for every system in this example, the 1,000 LUNs is counted toward the maximum visible limit of 1,200. (When disks and array LUNs are both used for storage, you can think of this as the device limit).

Disks are counted on a system-by-system basis toward the visible device limit. Therefore, the disks are counted toward the limit for the system to which the disks are connected, and not toward the visible device limit of any other systems.

For four systems in this example neighborhood, the number of visible devices is the same as or less than the visible device limit. However, if 1,000 array LUNs were presented to the neighborhood, you would not be able to connect 350 disks to system vs-B in HA pair 2. The reason is that the total of array LUNs and disks seen by system vs-B would be 1,350, which is more than the visible device limit of 1,200.

No more than 500 array LUNs and disks combined can be assigned to any one system in this example (so that the platform maximum assigned limit is not exceeded). However, you cannot assign 500 devices to each of the systems in the neighborhood because the total assigned devices would be 2,500. The combined assigned devices for the neighborhood cannot exceed the neighborhood LUN limit, so the total assigned devices must be 1,200 or less.