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# Set the SRDF GCM flag

SRDF groups provide a collective data transfer path linking volumes of two separate storage systems.

## Prerequisites

See Roles and associated permissions to determine the user roles that can perform this task.

## About this task

The Geometry Compatible Mode (GCM) parameter modifies how a storage system manages the size of a volume. When the GCM attribute is set, the volume is treated as 0.5 a cylinder smaller than its true configured size.

## Steps

1. Select the storage system.
2. Select Storage > Storage Volumes .
3. Select a storage volume and click Set SRDF GCM:
4. Click On to set the GCM flag or Off to unset the flag.

   | NOTE: The only way to unset this flag is to unmap the device which requires an outage at the host which would mean losing access to volumes.

5. Click OK.