IBM XIV Storage System Copy Services and Migration

7.6.1 Changing the synchronization rateThere is only one tunable parameter that determines the speed at which migration data istransferred between the XIV and defined targets. There are two other tunable parameters thatapply to XIV Remote Mirroring (RM):► max_initialization_rateThe rate (in MBps) at which data is transferred between the XIV and defined targets. Thedefault rate is 100 MBps and can be configured on a per-target basis. In other words, onetarget can be set to 100 MBps while another is set to 50 MBps. In this example a total of150 MBps (100+50) transfer rate is possible. If the transfer rate that you are seeing islower than the initialization rate, this may indicate that you are exceeding the capabilities ofthe non-XIV disk system to operate at that rate. If the migration is not being done withattached hosts off-line, consider dropping the initialization rate to a very low numberinitially to ensure that there that the volume of migration I/O does not interfere with otherhosts using the non-XIV disk system. Then slowly increase the number while checking toensure that response times are not affected on other attached hosts. If you set themax_initialization_rate to zero, then you will stop the background copy, but hosts will stillbe able to access all activated migration volumes.► max_syncjob_rateThis parameter (which is in MBps) is used in XIV remote mirroring for synchronizingmirrored snapshots. It is not normally relevant to data migrations. However, themax_initialization_rate cannot be greater than the max_syncjob_rate, which in turn cannotbe greater than the max_resync_rate. In general, there is no reason to ever increase thisrate.► max_resync_rateThis parameter (which is in MBps) is again used for XIV remote mirroring only. It is notnormally relevant to data migrations. This parameter defines the resync rate for mirroredpairs. Once remotely mirrored volumes are synchronized, a resync is required if thereplication is stopped for any reason. It is this resync where only the changes are sentacross the link that this parameter affects. The default rate is 300 MBps. There is nominimum or maximum rate. However, setting the value to 400 or more in a 4 Gbpsenvironment does not show any increase in throughput. In general, there is no reason toever increase this rate.Increasing the max_initialization_rate parameter may decrease the time required to migratethe data. However, doing so may impact existing production servers on the non-XIV storagedevice. By increasing the rate parameters, more outgoing disk resources will be used to servemigrations and less for existing production I/O. Be aware of how these parameters affectmigrations as well as production. You could always choose to only set this to a higher valueduring off-peak production periods.Chapter 7. Data migration 209