Veritas InfoScale™ 7.4.1 Virtualization Guide - Linux on ESXi
- Section I. Overview
- About Veritas InfoScale solutions in a VMware environment
- Section II. Deploying Veritas InfoScale products in a VMware environment
- Getting started
- Understanding Storage Configuration
- Section III. Use cases for Veritas InfoScale product components in a VMware environment
- Application availability using Cluster Server
- Multi-tier business service support
- Improving storage visibility, availability, and I/O performance using Dynamic Multi-Pathing
- How DMP works
- Improving data protection, storage optimization, data migration, and database performance
- Protecting data with InfoScale product components in the VMware guest
- Optimizing storage with InfoScale product components in the VMware guest
- Migrating data with InfoScale product components in the VMware guest
- Improving database performance with InfoScale product components in the VMware guest
- Setting up virtual machines for fast failover using Storage Foundation Cluster File System High Availability on VMware disks
- About setting up Storage Foundation Cluster File High System High Availability on VMware ESXi
- Configuring coordination point (CP) servers
- Section IV. Reference
About DMP I/O policies
The DMP I/O policy indicates how DMP distributes I/O loads across multiple paths to a disk array or enclosure. You can set the I/O policy for an enclosure (for example, HDS01), for all enclosures of a particular type (such as HDS), or for all enclosures of a particular array type (such as A/A for Active/Active, or A/P for Active/Passive).
The following policies may be set:
This policy attempts to maximize overall I/O throughput to or from the disks by dynamically scheduling I/O on the paths. It is suggested for use where I/O loads can vary over time. For example, I/O to or from a database may exhibit both long transfers (table scans) and short transfers (random look ups). The policy is also useful for a SAN environment where different paths may have different number of hops. No further configuration is possible as this policy is automatically managed by DMP. | |
Similar to the adaptive policy, except that I/O is scheduled according to the length of the I/O queue on each path. The path with the shortest queue is assigned the highest priority. | |
This policy is designed to optimize the use of caching in disk drives and RAID controllers. The size of the cache typically ranges from 120KB to 500KB or more, depending on the characteristics of the particular hardware. During normal operation, the disks (or LUNs) are logically divided into a number of regions (or partitions), and I/O from/to a given region is sent on only one of the active paths. Should that path fail, the workload is automatically redistributed across the remaining paths. You can use the size argument to the partitionsize attribute to specify the partition size. The partition size in blocks is adjustable in powers of 2 from 2 up to 231. A value that is not a power of 2 is silently rounded down to the nearest acceptable value. Specifying a partition size of 0 is equivalent to specifying the default partition size. The default value for the partition size is 512 blocks (256k). Specifying a partition size of 0 is equivalent to the default partition size of 512 blocks (256k). The default value can be changed by adjusting the value of the dmp_pathswitch_blks_shift tunable parameter. Note: The benefit of this policy is lost if the value is set larger than the cache size. For example, the suggested partition size for an Hitachi HDS 9960 A/A array is from 32,768 to 131,072 blocks (16MB to 64MB) for an I/O activity pattern that consists mostly of sequential reads or writes. | |
This policy sends I/O on paths that have the minimum number of outstanding I/O requests in the queue for a LUN. No further configuration is possible as DMP automatically determines the path with the shortest queue. | |
This policy is useful when the paths in a SAN have unequal performance, and you want to enforce load balancing manually. You can assign priorities to each path based on your knowledge of the configuration and performance characteristics of the available paths, and of other aspects of your system. | |
This policy shares I/O equally between the paths in a round-robin sequence. For example, if there are three paths, the first I/O request would use one path, the second would use a different path, the third would be sent down the remaining path, the fourth would go down the first path, and so on. No further configuration is possible as this policy is automatically managed by DMP. | |
This policy routes I/O down the single active path. This policy can be configured for A/P arrays with one active path per controller, where the other paths are used in case of failover. If configured for A/A arrays, there is no load balancing across the paths, and the alternate paths are only used to provide high availability (HA). If the current active path fails, I/O is switched to an alternate active path. No further configuration is possible as the single active path is selected by DMP. |