VERITAS Volume Manager 4.1 Release Notes (5900-0591, March 2010)

VERITAS Volume Manager 4.1 Release Notes
Known Problems and Workarounds
Chapter 1 31
• multiple FC10 disk systems connected to a single host through a hub
If the vxdmpadm disable ctlr=ctlr_name command is used for the above configurations to
disable I/O through a particular controller, I/O can be stopped through paths that were not
intended by the user.
If each FC10 disk system is individually connected to the host (using separate HBAs), the
above mentioned feature functions correctly and as expected.
DMP and JBOD Support
The Dynamic Multipathing feature on JBOD drives works only if the individual disks provide
unique serial number information. If the individual disks do not provide unique serial
numbers, even if the disks are configured for multipathing in hardware, the VxVM does not
provide multipathing support.
Usage of dmp_failed_io_threshold Parameter
Data loss can occur after the failure of a single path in a multipathed environment. This
might happen because of an interaction between an Application or file system and Volume
Manager. This issue applies to configurations in which:
• VxVM volumes are not mirrored.
• There are multiple paths to the disk.
• A portion of the I/O path below DMP fails in such a way that the error is not returned to
DMP before 10 minutes have elapsed. Examples of failures that have been seen to cause
this condition, include bad hardware (HBA, FCOT, GBIC, Switch Port, Array Controller)
and HBA reconfigured to retry endlessly.
NOTE A portion of the I/O path below DMP fails in such a way that the error is not
returned to DMP before 10 minutes have elapsed. Examples of failures that
have been seen to cause this condition, include bad hardware (HBA, FCOT,
GBIC, Switch Port, Array Controller) and HBA reconfigured to retry endlessly.
If the delay in returning the I/O is caused by a problem in the I/O path to the device rather
than the device itself, DMP will incorrectly return the error to the VxVM layer rather than
retrying the I/O on another path. If the volume is mirrored, VxVM will satisfy the I/O from the
other plex, and detach the plex that failed and prevented the volume from becoming hung.
If the volume is not mirrored, the error will be passed to the File System or application layer.
This can result in the File System marking inodes for deletion when they are still valid. If raw
volumes are in use, the application might believe that the data on the disk is corrupted when
it is actually clean.