Expert Oracle Exadata - Parent Directory

CHAPTER 7 RESOURCE MANAGEMENT Note: Metrics are collected for I/O requests to flash cache, flash-based grid disks, and physical disks (griddisks). However, IORM only manages I/O resources for physical disks, so metrics for the physical disks will be thefocus of this discussion.When a new collection is run, the previous set of metrics is moved to the METRICHISTORY object,where it is kept for a period of time. Metric history is retained for the number of days specified in theMETRICHISTORYDAYS attribute of cell, (the default is 7 days). For example, the next listing shows thatcellsrv will maintain a rolling history of 7 days.CellCLI> list cell attributes name, metricHistoryDaysenkcel01 7If you determine that 7 days is not sufficient history for your needs, you can modify the retention periodwith the CellCLI command alter cell. The following listing shows how you can change the retentionfor your storage cells to 14 days.CellCLI> alter cell metricHistoryDays='14'Cell enkcel01 successfully alteredCellCLI> list cell attributes name, metricHistoryDaysenkcel01 14Workload ManagementIORM metrics provide insight into how cellsrv is allocating I/O resources among the consumers in yourstorage grid. Cellsrv keeps track of I/O requests broadly categorized as “small requests” and “largerequests.” By comparing the large (LG) and small (SM) I/O requests in the IORM metrics, you candetermine whether your databases lean more toward a DW workload (high throughput) or an OLTPworkload (low latency). Oracle recently added a new option to the IORM plan called objective that tellsIORM to optimize the cell disk I/O queues for low latency, high throughput, or something in between.The IORM metric IORM_MODE was added to capture the objective in use during the collection period. Bycomparing the IORM_MODE with the actual workload on your storage cells, you can determine whether thecurrent IORM objective is appropriate or not. For example, if you find that a majority of I/O operationsin the storage cells are greater than 128K and thus large (LG), then IORM should be set to optimize forhigh throughput (objective=high_throughput). Oracle uses a threshold of 75% large I/O when the IORMobjective is set to auto, so that should give you an idea of what is meant by “majority.” For moreinformation on the IORM objective and possible settings, refer to the Workload Optimization sectionearlier in this chapter. The IORM_MODE metric can be observed using the following CellCLI command.CellCLI> list metriccurrent iorm_modeIORM_MODE enkcel01 0Possible settings for the IORM_MODE attribute are as follows:• 1, IORM objective was set to low_latency,• 2, IORM objective was set to balanced• 3, IORM mode was set to high_throughput221