Calculating server memory requirements

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It is important to determine the amount of memory that a server requires to run Copy Services Manager for a replication environment.

The Java heap size setting provides the maximum amount of memory that the server is allowed to use from the system memory. You can determine the maximum Java heap size setting by using the following table to calculate the maximum amount of memory that the configuration requires.

Note: The default maximum Java heap size is 1280 MB on stand-alone installations, 1024 MB on R8 and R9 HMC installations and 8192 MB on DS8000 10th Generation HMC installations. The minimum Java heap size on a z/OS environment is 1536 MB.
Table 1. Calculation for estimating the optimal Java heap size
Calculation for estimating the optimal Java heap size

Storage System Connection Memory usage (Mb) = Number of Storage Systems Connections * 66
Nonsession processing = 512 MB
Non-Safeguarded Copy sessions = 256 MB / 25,000 pairs
Note: The number of pairs for a session is the number of copy sets times the number of role pairs in the session. For more information, see the topic that is titled "Copy sets" in the online help documentation at https://www.ibm.com/support/knowledgecenter/SSESK4 Copy sets for more information.
Safeguarded Copy sessions = 0.8 KB * number of volumes * number of backups
Total optimal heap size = Nonsession + Non-Safeguarded Copy sessions + Safeguarded Copy sessions + Storage System Connection Memory usage
Example: The following scenario shows how to determine the necessary Java heap size for an environment like the one described:
Nonsession processing
512 MB
Note: All servers need 512 MB for nonsession processing.
Non-Safeguarded Copy sessions
A customer has a Global Mirror Failover or Failback DS8000® session with 15,000 copy sets. This session type has 3 role pairs. So, the total number of pairs in the session is 15,000 x 3, or 45,000 pairs. Looking at the table, 256 MB is needed for every 25,000 pairs. Therefore, the customer needs at least 512 MB to cover their 45,000 pairs.
Safeguarded Copy sessions
The customer also has a Safeguarded Copy session with 2000 volumes. If the customer wants to keep 250 backups for each of those 2000 volumes, then according to the table, the customer needs 2000 x 250 x 0.8 KB = 400,000 KB = 400 MB.
Adding up all the calculations gives 512 MB (nonsession) + 512 MB (non-Safeguarded Copy session) + 400 MB (Safeguarded Copy session) = 1424 MB. So, the customer needs at least 1424 MB of memory that is allocated to Copy Services Manager for processing. Because memory is allocated in chunks of 256 MB, the optimal Java heap setting for this configuration is 1536 MB.

If more memory is needed than the server's default, modify the maximum heap size by shutting down the Copy Services Manager server, adjusting the -Xmx parameter in the jvm.options file, and then restarting the server.

For distributed systems, the install dir/liberty/wlp/usr/servers/csmServer/jvm.options file holds the maximum heap size for distributed systems, and can be used to configure the session with the -Xmx parameter (for example, -Xmx1280m).

For z/OS systems, the path_prefix/opt/IBM/CSM/wlp/usr/server/csmServer/jvm.options file holds the maximum heap size for z/OS, and can be used to configure the session with the -Xmx parameter (for example, -Xmx1280m).

Recommended: When running Copy Services Manager on a DS8000 HMC, please follow the below guidelines.

If Copy Services Manager is running on an R8 or R9 DS8000 HMC, the default heap size is set to 1024 MB. If the memory calculation goes above 1024 MB, it is highly advisable that Copy Services Manager runs on an external server instead of the HMC.

For Copy Services Manager 6.2.10 and higher running on an HMC, if the HMC is configured with 32 GB, the maximum heap size is automatically set to 4096 MB. If the memory calculation goes above 4096 MB, it is highly advisable that Copy Services Manager runs on an external server instead of the HMC.

If Copy Services Manager is running on a DS8000 10th Generation HMC, the default heap size is set to 8192MB. If the memory calculation goes above 8192 MB, it is highly advisable that Copy Services Manager runs on an external server instead of the HMC.

When Copy Services Manager is running on a DS8000 10th Generation HMC, you can now create connections to as many DS8000 systems as needed, as long as the above calculation stays within the maximum 8192 MB.

Contact support if you have questions on where Copy Services Manager runs, and the heap size setting.

The optimal heap sizes are for ESESizer sessions with DS8000 volumes on microcode level 9.4 or higher, which use a new query that consumes fewer resources than older versions.

Table 2. Optimal Copy Services Manager Java heap size for ESESizer session (does NOT apply to SGC Sizer session).
Java heap size DS8000 capacity
4 GB <= 20 TiB
8 GB <= 60 TiB
16 GB > 60 TiB
Warning: It is not advisable to start an ESESizer session on a CSM server that is actively managing other sessions. Due to the heap requirements of the ESESizer session, the ESESizer session might affect the other sessions that currently run on the same server. DS8000 9.4 and Copy Services Manager 6.3.9.0 have a new SGC Sizer session which can collect data specifically for SGC Backup capacity measurements and does not require heavy system resources like the ESE Sizer session. It is still advisable though, to run the session on a server not managing others to prevent conflicts.

For more information about the maximum heap size, see the information about sizing the Java heap size in the IBM® SDK for Java Tools at https://www.ibm.com/developerworks/java/jdk/howdoi/index.html.

For more information about how to set up the Java heap size, see the WebSphere® Application Server V8.5 Liberty profile technote at http://www.ibm.com/support/docview.wss?uid=swg21596474.