default_disk_ir.5 (2010 09)

d
default_disk_ir(5)
OBSOLETE default_disk_ir(5)
(Kernel Tunable Parameter)
NAME
default_disk_ir - enable and disable use of device’s write cache in the SCSI subsystem (OBSOLETE)
VALUES
Failsafe
0 (off)
Default
0 (off)
Allowed values
0 (off) or non-zero (on)
Recommended values
0 (off)
DESCRIPTION
Note: This tunable is obsolete. HP no longer allows enabling, by default, write cache for all direct access
devices on the system. It is still possible to enable write cache for a specific device through the
scsictl
command. See scsictl (1M).
This tunable enables (1) or disables (0) the Immediate Reporting behavior of the SCSI subsystem, also
known as Write Cache Enable (WCE). With Immediate Reporting enabled, disk drives that have data
caches return from a
write() system call, including raw writes, when the data is cached, rather than
returning after the data is written to the media. This sometimes improves write performance especially
for sequential transfers.
Cached data can be lost if a device power failure or reset occurs before the device writes the cached data
to media. Because of these risks, the recommended value for this parameter on servers is Immediate
Reporting disabled (0).
Although not an option to the mount command, this tunable has a profound effect upon filesystem and
raw disk performance and, conversely, data integrity when system resets occur. This tunable also affects
delayed-write versus write-through-filesystem behavior.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable will take effect when the device is first opened.
When Should the Tunable Be Turned On?
When a third party application vendor recommends it. For normal use, HP strongly recommends you
don’t enable this tunable.
What Are the Side Effects of Turning the Tunable On?
Since enabling this tunable circumvents the protections provided by LVM or RAID, there is a strong risk
of filesystem corruption and data loss in case of a device power failure or reset.
When Should the Tunable Be Turned Off?
HP recommends you always disable this tunable. This is especially true if you don’t want to take the risk
of filesystem corruption and data loss in case of a device power failure or reset.
What Are the Side Effects of Turning the Tunable Off?
This might reduce the performance of disk write (not read) access while eliminating the risk of filesystem
corruption and data loss in case of a device power failure or reset.
What Other Tunables Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter has been obsoleted for HP-UX
11i Version 3.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1