Clarrion Storage

Snapview Clone and Snapview Snapshots

EMC SnapView is a storage-system-based software application that allows you to create a copy of a LUN by using either clones or snapshots. A clone is an actual copy of a LUN and takes time to create, depending on the size of the source LUN. A snapshot is a virtual point-in-time copy of a LUN which tracks differences to your original data, and takes only seconds to create.

SnapView has the following important benefits:

  • It allows full access to a point-in-time copy of your production data with modest impact on performance and without modifying the actual production data.
  • For decision support or revision testing, it provides a coherent, readable and writable copy of real production data.
  • For backup, it practically eliminates the time that production data spends offline or in hot backup mode. And it offloads the backup overhead from the production server to another server.
  • It provides instantaneous data recovery if the source LUN becomes corrupt. You can perform a recovery operation on a clone by initiating a reverse synchronization and on a snapshot session by initiating a rollback operation.

Clones

A clone is a complete copy of a source LUN. You specify a source LUN when you create a clone group. The copy of the source LUN begins when you add a clone LUN to the clone group. The software assigns each clone a clone ID. This ID remains with the clone until you remove the clone from its group.

While the clone is part of the clone group and unfractured, any production write requests made to the source LUN are simultaneously copied to the clone. Once the clone contains the desired data, you can fracture the clone. Fracturing the clone separates it from its source LUN, after which you can make it available to a secondary server.

Snapshot

A snapshot is a virtual LUN that allows a secondary server to view a point-in-time copy of a source LUN. You determine the point in time when you start a SnapView session. The session keeps track of the source LUN’s data at a particular point in time. A snapshot is a composite of the unchanged data chunks on the source LUN and data chunks on the reserved LUN.

During a session, the production server can still write to the source LUN and modify data. When this happens, the software stores a copy of the original point-in-time data on a reserved LUN in the reserved LUN pool. This operation is referred to as copy-on-first-write because it occurs only when a data chunk is first modified on the source LUN.

Create and activate a snapshot
01. Select the Source LUN to which the snapshot to be created. Start a SnapView Session. Provide a unique name to the SnapView Session. Once, the session is started, this will start copying the original data to Reserved LUN pool when ever the source LUN data is changed.

02. Create snapshot for the LUN. Give unique name for the snapshot. This snapshot is a virtual LUN that allows a secondary server to view a SnapView session. An active snapshot is a composite of a source LUN and reserved LUN data that lasts until you destroy the snapshot.

03. Add this snapshot to the appropriate storage group so that the hosts can access the snapshot.

04. Activate the snapshot. The Navisphere Manager activate option maps the snapshot to a SnapView session. The secondary server must be rebooted, or use some other means, so that this server recognizes the new device created when SnapView session started.

Deactivating a snapshot:
The deactivate option unmaps a snapshot from a SnapView session and destroys any secondary server writes made to the snapshot. The snapshot and session still exist but are not visible from the secondary server. The deactivate function is available only when a snapshot is active.

Stopping a SnapView session
Stopping a SnapView session ends the session’s point-in-time copy. Stopping the last SnapView session of a source LUN frees the reserved LUN(s) used by the session and any SP memory used to maintain the session image. The newly freed reserved LUN(s) becomes available for another session. Stopping a session also changes the snapshots' status from active to inactive.

Destroying a snapshot
If the snapshot is inactive, the software destroys only the selected snapshot.

If the snapshot is active, a warning message appears indicating that you should deactivate the snapshot before destroying it. If you accept the warning message, the software deactivates the snapshot, and destroys it (the snapshot) and any server writes made to the snapshot.

If the snapshot belongs to a storage group(s), an error message appears indicating that you cannot destroy a snapshot that is in a storage group. Remove the snapshot from the storage group(s), and then destroy the snapshot.

Navisphere Agent

Creating the Navisphere Agent file: agentID.txt
If you have a multihomed host and are running like :

  • IBM AIX,
  • HP-UX,
  • Linux,
  • Solaris,
  • VMware ESX Server (2.5.0 or later), or
  • Microsoft Windows

you must create a parameter file for Navisphere Agent, named agentID.txt

About the agentID.txt file:
This file, agentID.txt (case sensitive), ensures that the Navisphere Agent binds to the correct HBA/NIC for registration and therefore registers the host with the correct storage system. The agentID.txt file must contain the following two lines: 

 Line1: Fully-qualified hostname of the host
 Line 2: IP address of the HBA/NIC port that you want Navisphere Agent to use

For example, if your host is named host28 on the domain mydomain.com and your host contains two HBAs/NICs, HBA/NIC1 with IP address 192.111.222.2 and HBA/NIC2 with IP address 192.111.222.3, and you want the Navisphere Agent to use NIC 2, you would configure agentID.txt as follows: 

 host28.mydomain.com
 192.111.222.3

To create the agentID.txt file, continue with the appropriate procedure for your operating system:

For IBM AIX, HP-UX, Linux, and Solaris:

  1. Using a text editor that does not add special formatting, create or edit a file named agentID.txt in either / (root) or in a directory of your choice.
  2. Add the hostname and IP address lines as described above. This file should contain only these two lines, without formatting.
  3. Save the agentID.txt file.
  4. If you created the agentID.txt file in a directory other than root, for Navisphere Agent to restart after a system reboot using the correct path to the agentID.txt file, set the environment variable EV_AGENTID_DIRECTORY to point to the directory where you created agentID.txt.
  5. If a HostIdFile.txt file is present in the directory shown for your operating system, delete or rename it. The HostIdFile.txt file is located in the following directory for your operating system:
    AIX :- /etc/log/HostIdFile.txt
    HP-UX :- /etc/log/HostIdFile.txt
    Linux :- /var/log/HostIdFile.txt
    Solaris :- /etc/log/HostIdFile.txt
  6. Stop and then restart the Navisphere Agent.
    NOTE: Navisphere may take some time to update, however, it should update within 10 minutes.
  7. Once the Navisphere Agent has restarted, verify that Navisphere Agent is using the IP address that is entered in the agentID.txt file. To do this, check the new HostIdFile.txt file. You should see the IP address that is entered in the agentID.txt file.The HostIdFile.txt file is in the following directory for your operating system:
    AIX :/etc/log/HostIdFile.txt
    HP-UX :/etc/log/HostIdFile.txt
    Linux :-/var/log/HostIdFile.txt
    Solaris :-/etc/log/HostIdFile.txt

For VMware ESX Server 2.5.0 and later

  1. Confirm that Navisphere agent is not installed.
  2. Using a text editor that does not add special formatting, create or edit a file named agentID.txt in either / (root) or in a directory of your choice.
  3. Add the hostname and IP address lines as described above. This file should contain only these two lines, without formatting.
  4. Save the agentID.txt file.
  5. If you created the agentID.txt file in a directory other than root, for subsequent Agent restarts to use the correct path to the agentID.txt file, set the environment variable EV_AGENTID_DIRECTORY to point to the directory where you created agentID.txt.
  6. If a HostIdFile.txt file is present in the /var/log/ directory, delete or rename it.
  7. Reboot the VMWARE ESX server.
  8. Install and start Navisphere Agent and confirm that it has started.
    NOTE: Navisphere may take some time to update, however, it should update within 10 minutes.
  9. Once the Navisphere Agent has restarted, verify that Navisphere Agent is using the IP address that is entered in the agentID.txt file. To do this, check the new HostIdFile.txt file which is located in the /var/log/ directory. You should see the IP address that is entered in the agentID.txt file.

For Microsoft Windows:

  1. Using a text editor that does not add special formatting, create a file named agentID.txt in the directory C:/ProgramFiles/EMC/Navisphere Agent.
  2. Add the hostname and IP address lines as described above. This file should contain only these two lines, without formatting.
  3. Save the agentID.txt file.
  4. If a HostIdFile.txt file is present in the C:/ProgramFiles/EMC/Navisphere Agent directory, delete or rename it.
  5. Restart the Navisphere Agent
  6. Once the Navisphere Agent has restarted, verify that Navisphere Agent is using the correct IP address that is entered in the agentID.txt file. Either:
  7. In Navisphere Manager, verify that the host IP address is the same as the IP address that you you entered in the agentID.txt file. If the address is the same, the agentID.txt file is configured correctly.
  8. Check the new HostIdFile.txt file. You should see the IP address that is entered in the agentID.txt file.