2.3 File store considerations
The WebSphere Application Server transaction manager is responsible for storing information regarding the state of completing transactions in a persistent form that is used during transaction recovery. This persistent form is referred to as the transaction recovery log and is used to complete prepared transactions following a server failure. This activity is referred to as transaction recovery processing.
In addition to completing outstanding transactions, this processing also ensures that locks held in the associated resource managers are released. Prior to WebSphere Application Server V6, it was necessary to restart a failed server to perform recovery processing. Version 6.0 introduced the ability for a peer server (another cluster member) to process the recovery logs of a failed server while the peer continues to manage its own transactional workload.
This capability is known as peer recovery processing, and it supports the resolution of in-doubt transactions without the need to wait for the failed server to restart. This facility forms part of the overall WebSphere Application Server high availability (HA) strategy.
The basic requirement for transaction recovery requires the transaction recovery log to persist on a highly available file store. The file store is basically the file system it is placed in. The recommendation is to use hardware-based or software-based facilities to maximize the availability of the file systems themselves, such as the use of Storage Area Network (SAN). WebSphere Application Server V6.1 supports either cluster-managed or networked file systems.
Cluster-managed file systems use clustering and failover of shared disks to ensure high availability of files and directories.
Networked file systems use remote servers to store and access files as though they were local servers. Make sure that the file system in use supports access locking to ensure integrity of the file store components, particularly the log file, by the use of exclusive locks. IBM recommends that you use NFS V4.
For more information, refer to Transactional high availability and deployment considerations in WebSphere Application Server V6, which is available at the following address:
http://www-128.ibm.com/developerworks/websphere/techjournal/0504_beaven/0504_beaven.html