How to estimate the number of master servers needed

Article:HOWTO56073  |  Created: 2011-07-25  |  Updated: 2012-01-24  |  Article URL http://www.symantec.com/docs/HOWTO56073
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How to estimate the number of master servers needed

To determine how many master servers are required, consider the following:

  • The master server must be able to periodically communicate with all its media servers. If you have too many media servers, the master server may be overloaded.

  • Consider business-related requirements. For example, if an installation has different applications that require different backup windows, a single master may have to run backups continually. As a result, resources for catalog cleaning, catalog backup, or other maintenance activity may be insufficient.

  • As a rule, the number of clients (separate physical hosts) per master server is not a critical factor for NetBackup. The backup processing that clients perform has little or no effect on the NetBackup server. Exceptions do exist. For example, if all clients have database extensions, or all clients run ALL_LOCAL_DRIVES backups at the same time, server performance may be affected.

  • Plan your configuration so that it contains no single point of failure. Provide sufficient redundancy to ensure high availability of the backup process. More tape drives or media may reduce the number of media servers that are needed per master server.

  • Do not plan to run more than about 20,000 backup jobs per 12-hour period on a single master server.

    See the "Limits to scalability" item later in this topic.

  • Consider limiting the number of media servers that are handled by a master to the lower end of the estimates in the following table.

    A well-managed NetBackup environment may be able to handle more media servers than the numbers that are listed in this table. Your backup operations, however, may be more efficient and manageable with fewer, larger media servers. The variation in the number of media servers per master server for each scenario in the table depends on the following: number of jobs submitted, multiplexing, multiple data streams, and network capacity.

Table: Estimates of processors and memory for a master server

Number of processors

Minimum RAM

Maximum number of jobs per day

Maximum number of media servers per master server

2

4 GB

2000

20

4

8 GB

5000

50

8

16 GB

10000

100

These estimates are based on the number of media servers and the number of jobs the master server must support. This table is for guidance only; it is based on test data and customer experiences. The amount of RAM and number of processors may need to be increased based on other site-specific factors.

In this table, a processor is defined as a state-of-the-art CPU. An example is a 3-GHz processor for an x86 system, or the equivalent on a RISC platform such as Sun SPARC.

When making an estimate, consider the following:

  • Type of processor

    For a NetBackup master server, Symantec recommends using multiple discrete processors instead of a single multi-core processor. The individual cores in a multi-core processor lack the resources to support some of the CPU-intensive processes that run on a master server. Two physical dual-core processors (for a total of four processors) are better than a single quad-core processor.

  • Definition of a job

    For the purposes of Table: Estimates of processors and memory for a master server, a job is defined as an individual backup stream.

    Database and application backup policies, and the policies that use the ALL_LOCAL_DRIVES directive, usually launch multiple backup streams (thus multiple jobs) at the same time.

  • Limits to scalability

    Regardless of the size of the master server, the theoretical maximum rate at which backup jobs can launch is about one job per second. Therefore, a domain cannot run much more than 43,000 backup jobs in a 12 hour period.

    Note:

    Real world limitations make it unlikely that this theoretical figure can be achieved.

    Background: A NetBackup domain is defined as a number of NetBackup media servers and client computers under the control of a single NetBackup master server. A NetBackup domain may span multiple sites and datacenters . A single site or datacenter may consist of more than one NetBackup domain. Within a NetBackup domain, each backup job receives an identifier that includes a unique 10-digit UTC timestamp. As each timestamp must be unique, only one backup job can be launched per second, regardless of the resources available. As a result, a single NetBackup domain can launch a maximum of 86,400 backup jobs per day. In most situations, constraints within the hardware resources and infrastructure are likely to prevent the server from reaching the 86,400 limit. If a domain does not allow sufficient jobs, an environment can be configured to support multiple NetBackup domains.

See Designing your backup system


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