LUN sizing

Maximum and minimum LUN sizes

There are maximum and minimum LUN sizes the gateway supports:

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 a LUN

The usable space of a LUN size is modified by the following elements:

12.5%-Block checksum
10%-WAFL® (Write-Anywhere File Layout) reserve
1%- Core dump
20%-Snapshot (default setting)
Note
Space for your snapshot reserve is optional and 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

Note
One GB is equal to 1,000 x 1,024 x 1,024 bytes

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

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