NAME
vxfs_max_ra_kbytes — maximum amount of read-ahead data, in KB, that kernel may have outstanding for a single VxFS file system
VALUES
Default
1024
Specify an integer value or use an integer formula expression.
DESCRIPTION
When data is read from a disk drive, the system may read additional data
beyond that requested by the operation.
This "read-ahead" speeds up sequential disk accesses,
by anticipating that additional data will be read, and
having it available in system buffers before it is requested.
This parameter limits the number of read-ahead blocks that the kernel
is allowed to have outstanding for any given VxFS filesystem.
The limit applies to each individual VxFS filesystem,
not
to the system-wide total.
This parameter and
vxfs_ra_per_disk
work together to control the amount of read-ahead for VxFS filesystems.
The maximum read-ahead for VxFS filesystems is the lesser of:
vxfs_ra_per_disk * number_of_disks_in_logical_volume
and
vxfs_max_ra_kbytes
In general, larger values of
vxfs_max_ra_kbytes
improve sequential I/O performance.
EXAMPLE
With a 4-way parallel stripe of Seagate Barracuda 9GB drives,
good performance can be achieved with
vxfs_max_ra_kbytes
set to 1024 and
vxfs_ra_per_disk
set to 256.
WARNINGS
All HP-UX kernel tunable parameters are release specific.
This parameter may be removed or have its meaning changed in
future releases of HP-UX.
AUTHOR
vxfs_max_ra_kbytes
was developed by HP.
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