You can specify whether the host is denied access or continues to access the P-VOL when the pair is split due to an error. This is done with the Primary Volume Fence Level setting. You specify one of the following Fence Level options during the initial copy and resync operations. You can also change the Fence Level option outside these operations.
- Data – the P-VOL is fenced if an update copy operation fails. This prevents the host from writing to the P-VOL during a failure. This setting should be considered for the most critical volumes for disaster recovery. This setting reduces the amount of time required to analyze the consistency of S-VOL data with the P-VOL during disaster recovery efforts.
- Status – the P-VOL is fenced only if the primary system is not able to change S-VOL status to Suspend when an update copy operation fails. If the primary system successfully changes S-VOL pair status to Suspend, subsequent write I/O operations to the P-VOL will be accepted, and the system will keep track of updates to the P-VOL. This allows the pair to be resynchronized quickly. This setting also reduces the amount of time required to analyze S-VOL consistency during disaster recovery.
- Never – the P-VOL is never fenced. This setting should be used when I/O performance outweighs data recovery. "Never" ensures that the P-VOL remains available to applications for updates, even if all TrueCopy copy operations have failed. The S-VOL might no longer be in sync with the P-VOL, but the primary system keeps track of updates to the P-VOL while the pair is suspended. Host failover capability is essential if this fence level setting is used. For disaster recovery, the consistency of the S-VOL is determined by using the sense information transferred by host failover or by comparing the S-VOL contents with other files confirmed to be consistent.