DDS & Dynamic nsrmmd !!

Introduction to DDS

DDS controls application requests for tape media and allows the NetWorker server and all storage nodes to access and share all attached devices. A system administrator can configure DDS by setting a sharing policy for devices that are accessible from multiple storage nodes.

Two terms central to the use of DDS are drive and device. Within the context of DDS, these terms are defined as follows:

  • Drive — The physical backup object, such as a tape drive, disk, or file.
  • Device — The access path to the physical drive.

DDS is currently supported only in a storage area network (SAN) Fibre Channel environment and not in a direct-connect SCSI environment. Utilizing Dynamic Drive Sharing (DDS), individual drives in the library are controlled by more than one storage node. However, only one storage node can use a drive at any given time. Using DDS with a virtual tape library is not recommended.

Sharing libraries among NetWorker hosts

The NetWorker software permits different NetWorker hosts (a NetWorker server or storage node) within a datazone to control individual devices within a library. This is known as library sharing.

The presence of a SAN within the datazone is not required for library sharing.
Dynamic Drive Sharing (DDS) does not support sharing libraries across datazones.


Library sharing enables one NetWorker host to control the library’s robotic arm, while other NetWorker hosts (as well as the host controlling the robotic arm) can each control and use specific library devices. A specific device can be controlled only by a single NetWorker host. How library sharing works shows how multiple NetWorker hosts can share library devices.

Figure 12 How library sharing works

Dynamic nsrmmd :

The dynamic nsrmmd attribute in the NSR storage node attribute is off by default for the dynamic provisioning of nsrmmd processes. Turning on the dynamic nsrmmd attribute enables dynamic nsrmmd provisioning.
When the dynamic nsrmmd attribute is enabled and the number of sessions to a device exceeds the number of target sessions, the visible change in behavior is multiple nsrmmd processes on the same device. This continues until the max nsrmmd count, or max sessions values are reached, whichever is lower.

– Selected (dynamic mode): NetWorker starts one nsrmmd process per device and adds more only on demand, for example, when a device Target Sessions is reached.

– Unselected (static mode): NetWorker runs all available nsrmmd processes.


NetWorker starts one nsrmmd process per device and adds more only on demand, for example, when a device Target Sessions is reached. When backup target session is reached a new nsrmmd process will be created and next backup session is assigned to this nsrmmd process By enabling dynamic nsrmmd, only one nsrmmd process will be running when device is idle


To enable dynamic nsrmmd:

  1. Open NetWorker Management Console
  2. Click Devices
  3. Click Storage Node under Server Tree
  4. Click Properties
  5. Under storage node properties window, under General tab, Check mark “Dynamic nsrmmds”
  6. Click OK to save and close

To change number of dynamic nsrmmd on a device:

  1. On NMC device window select the device
  2. Right click on device and click Properties
  3. Under device properties window, click configuration
  4. Here under “Save Sessions”, change the “Max nsrmmd count” value
  5. Click OK to save and close



Service port requirements NetWorker storage node:

When calculating the service port requirements only consider devices that the storage node manages. To accommodate growth in the environment for example, the addition of new devices, allocate extra service ports for the NetWorker storage node.
The minimum number of service ports that a storage node requires is 5. This number includes the four TCP service ports required for a NetWorker client and one service port for the storage management process, nsrsnmd . NetWorker requires additional ports that differ depending on the device type used.Use these formulas to calculate storage node port requirements:

For NDMP-DSA or SnapImage devices:
5 + One service port for each backup stream

For tape devices:
5+ #devices + #tape_libraries

AFTD or Data Domain Boost devices:
5+ #nsrmmds

◆ #devices is the number of devices connected to the storage node.

◆ # tape_libraries is the number of jukeboxes that the storage node accesses. The storage node has one nsrlcpd process for each jukebox.

◆ #nsrmmds is the sum of the Max nsrmmd count attribute value of each device that the NetWorker storage node manages.



About Ahmad Sabry ElGendi
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