Example 6-1 shows how to change  gmlinktolerance  and the  gmmaxhostdelay  parameters using the  chsystem  command.  Test and monitor:  To reiterate, thoroughly test and carefully monitor the host impact of  any changes like these before putting them into a live production environment. A detailed description and settings considerations about the  gmlinktolerance  and the gmmaxhostdelay  parameters are described in 6.3.5, “1920 error” on page 203. rcbuffersize  was introduced with the version 6.2 code level so that systems with intense and  bursty write I/O would not fill the internal buffer while Global Mirror writes were undergoing  sequence tagging. Important:  Do not change the  rcbuffersize  parameter except under the direction of  IBM Support. Example 6-2 shows how to change  rcbuffersize  to 64 MB by using the  chsystem  command.  The default value for  rcbuffersize  is 48 MB and the maximum is 512 MB. Remember that any additional buffers you allocate are taken away from the general cache. IBM Spectrum Virtualize uses two parameters,  maxreplicationdelay  and  partnershipexclusionthreshold , for remote copy advanced tuning.  maxreplicationdelay  is a system-wide parameter that defines a maximum latency (in  seconds) for any individual write passing through the Global Mirror logic. If a write is hung for  that time, for example due to a rebuilding array on the secondary system, Global Mirror stops  the relationship (and any containing consistency group), triggering a 1920 error.  The  partnershipexclusionthreshold  parameter was introduced to allow users to set the  timeout for an I/O that triggers a temporarily dropping of the link to the remote cluster. The  value must be a number from 30 - 315. Important:  Do not change the  partnershipexclusionthreshold  parameter except under  the direction of IBM Support. A detailed description and settings considerations about the  maxreplicationdelay  parameter  are described in 6.3.5, “1920 error” on page 203. Example 6-2 Changing rcbuffersize to 64 MB Example 6-1 Changing gmlinktolerance to 30 and gmmaxhostdelay to 100 chsystem -gmlinktolerance 30 chsystem -gmmaxhostdelay 100 chsystem -rcbuffersize 64 rcbuffersize maxreplicationdelay and partnershipexclusionthreshold Chapter 6. Copy services  199