# Frequently Asked Questions for the Dell EMC PowerMax/VMAX3/VMAX/Symmetrix Storage Array

#### How many LUNs can be assigned to a single port?

A maximum of 255 LUNs can be assigned to any single port.

#### How can I use multiple device groups?

When you add a storage array, you can use only one Device Group per array entry. To use multiple device groups, configure one of the following additional settings:

- nDisableUseOfDG

- nDisableDGChange

Note

When using the registry keys, source and target devices will not be moved from the groups where they reside. Also, no new device groups will be created.

##### Scenario 1: Use the Device Group of the Source Device

Use the nDisableDGChange additional setting to use the device group of the source device instead of the device group that you defined in the CommCell Console for IntelliSnap operations. Before using this additional setting, ensure the target device is accessible from the same device group as the source device.

This additional setting is useful in the following scenarios:

- The device groups have different names on each client computer.

- The client computer has multiple device groups. Each device group has source-target device pairs.

##### Scenario 2: Use Target Device from Different Device Group

Use the nDisableUseOfDG additional setting to use a target device from a different device group other than the source device group. Enter the name of the of the devices group that contains the target devices in Arrays page.

This additional setting is useful when you have all target devices in one device group and the source devices are scattered across multiple device groups.

#### What is the precedence to select Business Continuance Volume (BCV) devices?

Commvault requires BCV and Symmetrix virtual device (VDEV) devices of the same block size to be created before performing IntelliSnap operations. The BCV device selection occurs based on the following precedence:

1. Currently established BCVs

2. Masked BCV’s to a proxy or source that are currently established

3. Split source BCVs

4. Split source BCVs masked to a proxy or source

5. Non-established BCVs

#### How many BCV devices are required to perform the IntelliSnap operation?

Use the following matrix to calculate the number of target devices required for performing IntelliSnap operations.

Agent | Target Device Requirements (Business Continuance Volumes/ Shadow Image Volumes) | NOTES

| full backup | incremental backup | differential backup |
DB2 | [Number of devices where data resides] + [Number of devices where the online log resides] + [Number of devices where the 'LOCAL_DB_DIRECTORY' resides] + [Number of devices where the 'DBPATH' resides] | N/A | N/A |
Exchange Database | [Number of devices where data resides] + [Number of devices where the log resides] | [Number of devices where the log resides] | [Number of devices where the log resides] | For example, if your data resides on 2 devices, logs reside on 1 devices. Full backup will require 3(2+1) target devices, Incremental/Differential backup will require 1 target devices.
Microsoft SQL Server | [Number of devices where data resides] + [Number of devices where the log resides] |  | [Number of devices where data resides] + [Number of devices where the log resides] | For example, if your file system data resides on 3 devices you will require 3 target devices. SQL log backup does not require any target device.
Microsoft Windows File System | Number of devices on which the file system data resides | Number of devices on which the file system data resides | Number of devices on which the file system data resides |
NAS NDMP | Number of devices on which the file system data resides |  |  |
Oracle | [Number of devices where data resides] + [Number of devices where the log resides] |  | N/A |
Oracle – Data and logs residing on the same devices | 2x[Number of devices where data and logs reside] |  | N/A | For example, if your data and logs reside on 3 devices, you will require 6 target devices.
Applications running on JFS | [Number of devices where application data resides] + [Number of devices where JFS logs reside] + [No. of devices on which logs reside] |  | N/A | For example, if your application data resides on 2 devices, logs reside on 1 devices, data and logs share one device, and JFS logs reside on 1 device, you will require 6 (2+1+2+1) target devices
SAP for Oracle - Data and logs | [Number of devices where data resides] + [Devise where the 'sapbackup' directory resides] + [Number of devices where the log resides] + [Device where the 'saparch' directory resides] + 2 x [Device where the 'dbs' directory resides] | N/A | N/A |
UNIX File System | [Number of devices where data resides] + [Number of devices where the log resides] |  |  |
UNIX File System on JFS | [Number of devices on which the file system data resides ] + [No. of devices on which file system logs reside] |  |  | For example, if your file system data resides on 2 devices and file system log resides on 1 device, you will require 3 target devices.
VMware | Number of luns on which the datastore for the VM resides | Number of luns on which the datastore for the VM resides | N/A |
Microsoft Hyper-V | Number of luns on which vhd and configuration files of VM reside | Number of luns on which vhd and configuration files of VM reside | N/A |

#### How do I verify if a LUN is mapped to a host computer that requires protection?

To check if you assigned a LUN to the host computer, run the following command on the host computer:

    C:\> symdev -sid $[symm_ID]

The physical device name might be displayed as "Not Visible". This may happen if you have multiple host computers that are doing the device management or if you didn't refresh the SYMAPI DB. You can try the following:

- Check the Device Manager and kernel Messages to ensure the disk is accessible.

- Refresh the SYMAPI DB using the following command:

      C:\> symcfg discover

If you still see the same message, then configure or map the LUN to the host adapter to make it accessible to the production host computer.

#### How does the IntelliSnap feature work with the TimeFinder Mirror software?

Commvault software runs the incremental establish operation on BCV volumes, except for the first time that the TimeFinder backup operation runs on the BCV, which is a full backup operation.

Assuming that device #006C is used as the Primary LUN to the production host, the following steps describe how to create a new TimeFinder Mirror relationship with IntelliSnap:

1. Create a new device group to be used for IntelliSnap backup.

2. Assign the BCV volumes to the device group created in (a).

        C:\> symbcv –g $[deviceGroup] associate dev $[nnnn]

3. Using the CommCell Console, create a new subclient for the LUN:

   - During the subclient configuration, select EMC TimeFinder BCV as the storage array.

   - Run a Full/Incremental backup job.

4. During the IntelliSnap backup job, the device group gets created, and during the snapshot creation, a synchronization is performed.

   A BCV device cannot split until the synchronization completes. You can if the device is ready to split using the following command:

   C:\> symmir -g test split

5. Once the synchronization completes, the "split" operation is automatically issued by the Commvault software.

6. During the cataloging phase, the host LUN mapping is adjusted for the BCV device.

7. The BCV device is un-masked. From the CommCell Console, you can see the snapshots created during the IntelliSnap job.

#### How does IntelliSnap work with TimeFinder Snap?

Similar to TimeFinder Mirror, Commvault always require a new or recycled VDEV relationship to a single Production volume for each IntelliSnap job. However, TimeFinder Snap allows the LUN to be available to the production host by using the Copy-On-Write mechanism.

Assuming that device #0094 is used as the Primary LUN to the production host, the following steps describe how to create a new TimeFinder/Snap relationship with IntelliSnap:

1. Create a new Device Group "test" to be used for IntelliSnap.

2. You must have a SAVE pool for VDEV volumes. You may use the DEFAULT_POOL.

   In the example shown on the right, you can see that the DEFAULT_POOL has few devices and plenty of space. If you require further SAVE devices, you can create a text file (e.g., new_save_pool.txt) with the following content:

       add dev $[81:82] to pool $[DEFAULT_POOL], type=savedev, member_state=$[enable];

   After creating the text file, run the following commands to add the extra devices to the SAVE:

       C:\> symconfigure -sid $[0546] -f $[c:\new_save_pool.txt] -v -nop $[commit]

3. Assign a VDEV volume to be used for TimeFinder Snap.

4. Using the CommCell Console, create a new subclient for the LUN:

   - During the subclient configuration, ensure to select EMC TimeFinder Snap as the storage array.

   - Run a Full/Incremental backup job.

   During the snapshot creation, Copy-On-Write operations are performed.

   Once the snapshot is created, the snapshot will be mounted and cataloged, and the VDEV device will be "un-masked".

#### What SYMCLI environment variables can I use?

There are many environment variables that might aid in troubleshooting and potentially change some of the IntelliSnap behavior. Consult with your EMC Storage Consultant and use these variables with caution.

Use the following command to retrieve the list of SYMCLI variables:

    C:\> symcli -env

#### If I have RDF devices that are not paired, how can I use them for IntelliSnap backup?

To use Remote Data Facility (RDF) devices that are not paired, follow the steps given below:

1. Create an RDF device group.

2. Ensure that the source RDF device is in the device group on the same computer.

3. Add the target VDEV/BCV to the same device group. Use the symdg add with -tgt option to add the target devices to the RDF device group.

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