About Shared Storage Option components
The NetBackup Enterprise Media Manager (EMM) service manages media information. The Enterprise Media Manager also is the device allocator (DA) for shared drives.
Figure: Shared Storage Option example shows an example of a shared drive configuration.
The following items describe the NetBackup components for the Shared Storage Option example in Figure: Shared Storage Option example.
The master server hosts the Enterprise Media Manager (EMM) service. It's the device allocation host.
Host A:
Is a NetBackup media server that runs the Automatic Volume Recognition (avrd) process, the NetBackup Device Manager service (ltid), and the NetBackup Volume Manager (vmd) service.
Is connected to drives DRV1 and DRV2 through SAN hardware.
Is the first host in the environment to come online with a non-zero scan ability factor. Therefore, it's the initial scan host for its drives.
See About scan hosts.
Host B:
Is a NetBackup media server that runs the Automatic Volume Recognition (avrd) process, the NetBackup Device Manager service (ltid), and the NetBackup Volume Manager (vmd) service.
Is connected to drives DRV1 and DRV2 through SAN hardware.
Controls the robotics. Except for ACS or TLM robot types, only one robot control host exists for each robot.
For a process flow diagram of Shared Storage Option components, see the NetBackup Logging Reference Guide:
http://www.veritas.com/docs/DOC5332
The NetBackup Enterprise Media Manager (EMM) service allocates devices for Shared Storage Option jobs and tasks. The EMM service runs on the NetBackup master server. The host that allocates devices is also known as the device allocation host.
To coordinate network-wide allocation of tape drives, the NetBackup Enterprise Media Manager (EMM) service manages all shared tape requests in a shared drive environment. EMM responds to requests from a single NetBackup master server for its corresponding media servers, and NetBackup SAN media servers within a single NetBackup domain.
EMM maintains shared drive and host information. Information includes a list of hosts that are online and available to share a drive and which host currently has the drive reserved. The Media Manager device service (ltid) requests shared drive information changes.
Scan hosts are a component of the NetBackup Shared Storage Option.
Each shared drive has a host that is identified as the scan host. A scan host is the host from which the automatic volume recognition process (avrd) scans unassigned drives. (The robotic daemons scan assigned drives.) A scan host must have data path access to the drive.
The EMM database contains the shared drive information; that information includes the scan host. Media servers receive drive status information from the EMM service.
How the scan host is determined | EMM determines scan hosts; a scan host may be different for each shared drive. The first host in the environment to come online with a non-zero scan ability factor is the initial scan host for its drives. To configure the scan ability factor of media servers, use the nbemmcmd command. For more information, see the NetBackup Commands Reference Guide, available at the following URL: |
The scan host can change | A scan host is assigned for a shared drive until some interruption occurs. For example, if one of the following occurs, EMM chooses a new scan host:
The scan host temporarily changes to hosts that request tape mounts while the mount is in progress. Scan host changes occur so only one host at a time has access to the drive path. |
Drive paths for the scan host | If a drive has multiple paths that are configured on the selected scan host, EMM selects a scan path as follows:
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Shared tape drive polling | For shared tape drives, only the scan host polls drives until a mount request is received from NetBackup. During a mount request, NetBackup uses the host that requests the mount to poll the shared drive. This design enables NetBackup to support Dynamic Loop Switching or SAN zones. Each tape drive needs to be detected only from a single host. Each tape drive can potentially have its own scan host that switches dynamically to process errors and continue availability. A central device arbitrating component manages scan host assignments for shared drives. The arbitrating component also provides a network drive reservation system so that multiple NetBackup media servers can share a drive. Polling a shared tape drive allows dynamic loop switching and reduces the number of device accesses and reduces CPU time. However, it cannot detect connectivity breaks (for example, discontinuity in the Fibre Channel fabric) until I/O occurs. |
SAN media servers are NetBackup media servers that back up their own data. SAN media servers cannot back up the data that resides on other clients.
SAN media servers are useful for certain situations. For example, a SAN media server is useful if the data volume consumes so much network bandwidth that it affects your network negatively.
When you define a backup policy for a SAN media server, add only the SAN media server as the client.
The NetBackup Shared Storage Option can use NetBackup SAN media servers.