Plan file system support on Multiplatforms

Queue manager data is stored in the file system. A queue manager makes use of file system locking to prevent multiple instances of a multi-instance queue manager being active at the same time.

Shared file systems

Shared file systems enable multiple systems to access the same physical storage device concurrently. Corruption would occur if multiple systems accessed the same physical storage device directly without some means of enforcing locking and concurrency control. Operating systems provide local file systems with locking and concurrency control for local processes; network file systems provide locking and concurrency control for distributed systems.

Historically, networked file systems have not performed fast enough, or provided sufficient locking and concurrency control, to meet the requirements for logging messages. Today, networked file systems can provide good performance, and implementations of reliable network file system protocols such as RFC 3530, Network File System (NFS) version 4 protocol, meet the requirements for logging messages reliably.

Shared file systems and IBM MQ

Queue manager data for a multi-instance queue manager is stored in a shared network file system. On Microsoft UNIX, Linux , and Windows systems, the queue manager's data files and log files must be placed in shared network file system. On IBM® i, journals are used instead of log files, and journals cannot be shared. Multi-instance queue managers on IBM i use journal replication, or switchable journals, to make journals available between different queue manager instances.

Prior to release v7.0.1, IBM MQ does not support queue manager data stored on networked storage accessed as a shared file system. If queue manager data is placed on shared networked storage, then you need to ensure the queue manager data is not accessed by another instance of the queue manager running at the same time.

From v7.0.1 onwards, IBM MQ uses locking to prevent multiple instances of the same multi-instance queue manager being active at the same time. The same locking also ensures that two separate queue managers cannot inadvertently use the same set of queue manager data files. Only one instance of a queue manager can have its lock at a time. Consequently, IBM MQ does support queue manager data stored on networked storage accessed as a shared file system.

Because not all the locking protocols of network file systems are robust, and because a file system might be configured for performance rather than data integrity, you must run the amqmfsck command to test whether a network file system will control access to queue manager data and logs correctly. This command applies only UNIX and IBM i systems. On Microsoft Windows, there is only one supported network file system and the amqmfsck command is not required.