Create snapshot – EMC VNX

Posted By Rajesh Radhakrishnan February 03 2018

Creating a snapshot does not consume any pool space. The space starts being used when new writes to the primary LUN or to the snapshot itself arrive. Snapshots have a granularity of 8 KB, and their blocks are tracked just like the blocks in thin LUNs. Every snapshot must have a primary LUN, and that property never changes.A primary LUN cannot be deleted while it has snapshots. In Unisphere,You can delete a LUN that has snapshots by selecting an optional setting that deletes the snapshots first.

A pair of VNX Snapshots

Before creating a snapshot, use the SnapCLI utility to flush the host buffers.

:: Windows
SnapCLI flush -o G:

Create a snapshot

  • In Unisphere, select Storage > LUNs

Create VNX Snapshots in Unisphere

  • Click Create Snapshot or right-click the primary LUN

# To create snapshot in the CLI

naviseccli snap -create -res 1 -name “cli_snap” -descr “snap created via CLI”
# ^^^
# LUN ID

Note: When a snapshot is first created, it is write-protected

Unisphere view of the VNX Snapshot write protection

When you try to attach a snapshot that has the Allow Read/Write option disabled, Unisphere automatically enables it and displays a warning.

Unisphere VNX Snapshot Attach warning

If a Snapshot is attached from the CLI, then the -allowReadWrite property must be set to “Yes”. Therefore, you must manually modify it prior to an attach command.

# To modify a snap in the CLI

naviseccli snap -modify -id “cli_snap” -allowReadWrite yes

See How to create Snapshot Mount Point