Oracle ZFS Storage Appliance: Disabling Write Cache Enable (WCE) for ZFSSA Exported LUNs on Solaris Clients (Doc ID 2063355.1)

Last updated on SEPTEMBER 30, 2022

Applies to:

Goal

To permanently disable Write Cache on LUNs exported from an Oracle ZFS Storage Appliance when used in a zpool on a Solaris client.

Background:

ZFS enables the write cache on pool devices upon zpool import, and safely handles cache flushing in the event of a system power loss. However, a power-on-reset condition can potentially occur while data has not yet been committed to stable storage.

In an environment with no single point of failure, this situation is automatically detected and corrected by ZFS the next time the data is read. Routine pool scrubs of the pool can increase the detection and repair of any lost writes.

In an environment with a single point of failure, this problem could lead to data loss.

This problem might also occur more frequently when accessing LUNs that are exported from a clustered configuration. During cluster failover, data cached by the failing head may be lost due to a power-on-reset event that is explicitly sent by the SCSI target on the surviving head. In this situation, even pools with no single point of failure might be affected.

A symptom of this issue is clusters of persistent checksum errors. You can use the output from fmdump –eV to determine whether the checksum errors have been diagnosed as persistent. The zio_txg entry in the fmdump –eV output represents the time that a block of data is written. Note that a pattern of persistent checksum errors could also be a symptom of failing devices, software, or hardware.

Solution

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