GPFS configuration attributes for DMAPI

GPFS uses several attributes for DMAPI that define various timeout intervals. These attributes can be changed with the mmchconfig command.

The DMAPI configuration attributes are:

dmapiDataEventRetry

Controls how GPFS handles the data event when it is enabled again right after this event is handled by the DMAPI application. Valid values are:

-1: Specifies that GPFS will always regenerate the event as long as it is enabled. This value should only be used when the DMAPI application recalls and migrates the same file in parallel by many processes at the same time.
0: Specifies to never regenerate the event. This value should not be used if a file could be migrated and recalled at the same time.
Positive Number: Specifies how many times the data event should be retried. The default is 2, which should be enough to cover most DMAPI applications. Unless a special situation occurs, you can increase this to a larger number or even set this to -1 to always regenerate the events. Unless you perform careful testing, IBM® recommends that you never change the default setting.

dmapiEventTimeout

Controls the blocking of file operation threads of NFS, while in the kernel waiting for the handling of a DMAPI synchronous event. The parameter value is the maximum time, in milliseconds, the thread will block. When this time expires, the file operation returns ENOTREADY, and the event continues asynchronously. The NFS server is expected to repeatedly retry the operation, which eventually will find the response of the original event and continue. This mechanism applies only to read, write, and truncate events, and only when such events come from NFS server threads.

The timeout value is given in milliseconds. The value 0 indicates immediate timeout (fully asynchronous event). A value greater than or equal to 86400000 (which is 24 hours) is considered 'infinity' (no timeout, fully synchronous event). The default value is 86400000. See also Support for NFS.

For the parameter change to take effect, restart the GPFS daemon on all nodes.

dmapiFileHandleSize

Controls the size of file handles generated by GPFS. The default DMAPI file handle size is 32 bytes. For clusters created prior to GPFS 3.2, the default DMAPI file handle size is 16 bytes.

Note: To change the DMAPI file handle size, GPFS must be stopped on all nodes in the cluster.

dmapiMountEvent

Controls the generation of the mount, preunmount, and unmount events. Valid values are:

all: Specifies that mount, preunmount, and unmount events are generated on each node. This is the default behavior.
LocalNode: Specifies that mount, preunmount, and unmount events are generated only if the node is a session node.
SessionNode: Specifies that mount, preunmount, and unmount events are generated on each node and are delivered to the session node, but the session node will respond with DM_RESP_CONTINUE to the event node without delivering the event to the DMAPI application, unless the event is originated from the SessionNode itself.

dmapiMountTimeout

Controls the blocking of mount operations, waiting for a disposition for the mount event to be set. This timeout is activated at most once on each node, by the first mount of a file system which has DMAPI enabled, and only if there has never before been a mount disposition. Any mount operation on this node that starts while the timeout period is active will wait for the mount disposition. The parameter value is the maximum time, in seconds, that the mount operation will wait for a disposition. When this time expires and there still is no disposition for the mount event, the mount operation fails, returning the EIO error.

The timeout value is given in full seconds. The value 0 indicates immediate timeout (immediate failure of the mount operation). A value greater than or equal to 86400 (which is 24 hours) is considered 'infinity' (no timeout, indefinite blocking until there is a disposition). The default value is 60. See also Mount and unmount and Initializing the Data Management application.

dmapiSessionFailureTimeout

Controls the blocking of file operation threads, while in the kernel, waiting for the handling of a DMAPI synchronous event that is enqueued on a session that has suffered a failure. The parameter value is the maximum time, in seconds, the thread will wait for the recovery of the failed session. When this time expires and the session has not yet recovered, the event is aborted and the file operation fails, returning the EIO error.

The timeout value is given in full seconds. The value 0 indicates immediate timeout (immediate failure of the file operation). Start of change The value must be less than or equal to 86400 (which is 24 hours) because after that the failed session will be discarded. End of change The default value is 0. See also Failure and recovery of IBM Storage Scale Data Management API for GPFS for details on session failure and recovery.