Upon completion of this module, you should be able to:
Describe how data assignment planning can improve system performance
List the volume configurations that can improve read and write performance
List the SSVM commands that are used to gather performance information
Describe the three types of RAID5 write procedures
List the three types of RAID5 write procedures in order of performance efficiency
Performance Guidelines
Several strategies can be used to optimize volume performance including:
Assigning data to physical drives so that the I/O load is balanced amont them
Increasing the access bandwidth to data by using striping,mirroring or RAID5
Increasing the access bandwidth to data by cabling across system boards and controllers
To provide potimal read performance for different types of mirrored volumes, SSVM supports the following read policies:
1,The round-robin read policy(round)
Read requests to a mirrored volume are satified in a round-robin manner from all plexes in the volume.This is selected when there is no signficant performance advantage by using any particular mirror
2,The preferred-plex read policy(prefer)
Read requests to a mirrored volume are satisfied from one spedific plex(presumably the plex with the highest performance),unless that plex has failed
3,The default read policy(select)
The appropriate read policy is automatically selected for the configuration; for example, selecting preferred-plex when there is only one striped plex associated with the volume and round-robin in most other cases
Performance Monitoring
The SSVM software continuously gathers statistical information which can be evaluated using:
The vxstat command
The vxtrace command
Performance Analysis
The SSVM performance analysis process includes the following steps:
1,Resetting the existing data
2,Maintaining normal system load during evaluation
3,Identifying SSVM objects with an unusually large number of I/O operations
4,Identifying SSVM objects with excessive read or write times
5,Performing detailed traces using the vxtrace command
RAID5 Write Performance
To maximize write performance in RAID5 volumes you must understand the following write operations and how they affect performance:
Read-modify-write
Reconstruct-write
Full-stripe write
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