Drain

The primary function of the drain operation is to determine how the board's memory is to be vacated by the operating environment and, if required, to select a target memory area for copying the nonpageable memory on a board. If a suitable target memory area is not available when the drain operation is requested, the request is denied. If the drain is rejected for this reason, you can continue to retry until target memory is available. Refer to "Configuration for DR Detach" in the Sun Enterprise 10000 DR Configuration Guide.

After the drain operation is started, the pageable memory on the board is flushed to a disk, which removes it from use by the domain. Whenever a page of memory becomes free, that page is locked from further use. The drain has no noticeable impact on the processes using the CPU and I/O resources on the board. However, less memory is available to the domain.

After memory is drained, enough memory and swap space must remain in the domain to accommodate the current workloads.

During the drain period, Hostview and dr(1M) are available to monitor the detach progress. You can view the current status of the drain operation, including the number of memory pages remaining to be drained, and the usage of devices on the board. With this information, you can prepare the domain for detaching the remaining board devices.

If you decide not to proceed with the detach operation, you can abort the operation, and the memory on the board is returned to regular usage. You can also abort the operation during the drain process or after the drain has been completed. If extreme memory pressure exists during the drain, you will see little, or no, progression in the percentage of drained pages, and you may want to abort the drain and wait until the workload on the domain has decreased, enabling it to accommodate the reduction in memory.

The drain operation is complete when all of the memory pages are free from usage. You can then complete the detach operation.