Rules for configuring gateways to your storage subsystem

About configuration rules

You must follow these rules when configuring LUNs to your gateway.

Maximum total capacity attached to a gateway

Gateway models have the following maximum total capacity limits.

Gateway model	Maximum total capacity
GF270c	6 TB
GF825	3 TB
GF825c	6 TB
GF920	6 TB
GF920c	12 TB
GF940	12 TB
GF940c	24 TB
GF960	24 TB
GF960c	48 TB

Minimum total capacity attached to a gateway

Gateway models have the following minimum total capacity limits.

Gateway model	Minimum total capacity
GF270c	1.5
GF825	68 GB
GF940/GF960	272 GB

Connection to multiple storage subsystems

Multiple storage subsystems can connect to a stand-alone or clustered gateway if the storage subsystems are within the same series.

You can connect to multiple storage subsystems using the same configurations described in Chapter 3, Supported Configurations.

Maximum number of unique LUNs per gateway

A gateway can have up to the following number of unique LUNs.

Gateway model	Maximum number of unique LUNs
GF270c	42 (21 on each cluster node)
GF825	84
GF825c	168 (84 on each cluster node)
GF920	168
GF920c	336 (168 on each cluster node)
GF940	336
GF940c	672 (336 on each cluster node)
GF960	336
GF960c	672 (336 on each cluster node)

Minimum number of LUNs per gateway

A gateway must have at least one LUN. A cluster configuration must have at least two LUNs.

Note
The GF270c requires a minimum of two LUNs: one for the root volume and one for core dumps.

LUN sizes

The gateway has restrictions on the maximum and minimum size LUN supported.

Maximum LUN size

The maximum LUN size supported is 500 GB.

Minimum LUN size

The minimum LUN size supported is 1 GB.

Usable space on LUNs

LUN size is affected by the following elements:

12.5%-Checksum
10%-WAFL® (Write-Anywhere File Layout) reserve
1%-Core dump
20%-Snapshot (default setting)
Note
Space for your snapshot reserve is changeable through Data ONTAP.

Determining LUN size

You can determine LUN size in the following respects:

Usable capacity (the actual capacity available for storage)
Desired capacity (the exact LUN size desired)

Calculating the usable capacity

To determine the usable capacity for storage in a LUN, after taking into account Snapshot reserve, use the following formula, where Y is the usable capacity for storage and N is the total capacity of the LUN.

Y = N x {0.875 x 0.9 x 0.99 x Snapshot reserve}

Example

Total capacity of LUN is 4 GB with Snapshot reserve set at default:

4 x {0.875 x 0.9 x 0.99 x 0.8} = 2.49 GB

Calculating desired capacity

To determine the LUN capacity needed to obtain the desired capacity, while taking reserved space into account, use the following formula, where Y is the exact desired LUN size:

Y divided by {0.875 x 0.9 x 0.99 x Snapshot reserve} = Actual capacity needed

Note
This formula does not take into account space for Snapshot reserve, which you should include for achieving the LUN size desired.

Example

Desired LUN capacity is 10 GB of usable capacity.

Calculating actual LUN size without accounting for Snapshot reserve.

10 GB divided by {0.875 x 0.9 x 0.99} = 13.3 GB

Snapshot reserve left on default setting.

10 GB divided by {0.875 x 0.9 x 0.99 x 0.8} = 16 GB