Tuning disk I/O-bound systems
If the system is
because of disk activity,
there are a number of things that can be done:
Replace the existing disks with faster versions.
Filesystems that are used to hold temporary files can be
in memory. (See
for more information.)
This has the disadvantage of taking memory away from
applications but it can be extremely effective
in improving I/O throughput.
Upgrade the disk controller to a type that supports block or track caching,
and scatter-gather read/writes.
For SCSI disks, upgrade the host adaptor to one that
supports caching, scatter-gather, and tagged command queuing.
Where possible, use fast SCSI subsystems with wide data
If the system is running a disk-intensive application such
as a database, having multiple host adapters (for
SCSI), disk controllers and
disks will help speed up access to data by reducing contention.
Spread filesystems and
across different disks and/or
buses to help spread the load. Alternatively, you can use
software to balance the load across several disks.
For a comparison of the various configurations
that are available using virtual disks see
``About virtual disks''.
You may find that the performance of the system can be improved
slightly by increasing the values of the BDFLUSHR and
NAUTOUP kernel parameters.
This will reduce the number of times
the disk will be accessed because blocks can be updated
more often in memory before they are written to the disk.
The inherent risk is that more data will be lost if the
system crashes because it will be longer since it was last
written to the disk. It is considered good practice to protect
mission-critical systems against power failure using a
UPS or similar device.
Various disk organization strategies are discussed in
``Overcoming performance limitations of hard disks''
which includes suggestions for optimizing your current hardware
Disk manufacturers implement various hardware and firmware
(software in the disk controller) strategies to improve disk
performance. These include track caching and varying the number of disk
blocks per track across the disk surface. Usually, you have no
control over such features.
SCSI disk driver request queue
Identifying disk I/O-bound systems
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003