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Managing Shared Disks

Application programming considerations for Hashed Shared Disks

Read this section for information on application programming performance with Hashed Shared Disk and on how to use Hashed Shared Disks through C language interfaces.

Allocating I/O buffers

The address of your I/O buffer must be aligned on a 4KB boundary. If it is not, the Hashed Shared Disk read and write routines will not parallelize I/O requests to underlying virtual shared disks. Performance will be less than optimal.

Set the environment variable MALLOCTYPE to 3.4 to make all new allocated buffers (MALLOC) at the page boundary.

Getting Hashed Shared Disk information with C interfaces

The Hashed Shared Disk base code has a sample directory: /usr/lpp/csd/samples.

This directory contains the following files:

When compiled, this file generates a binary that shows hashed shared disk information for the hsd_name given from the command line.

When compiled, this file generates a binary that lists information for all configured hashed shared disks.
The header file /usr/include/hsd_ioctl.h is installed with the ssp.csd.hsd image. Structures defined in hsd_ioctl.h may change from release to release. This may require that you recompile your applications that utilize C interfaces to the HSD to run on new releases. If you see IOCTL failures in your application after migrating to a new release, try recompiling the application.

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