Configuring kernel SCSI parameters

You can reduce the time needed to perform jobs that have substantial I/O by changing certain files within your application.

The two procedures described in Procedure A and Procedure B can be performed to shorten the processing time of large I/O directed to one SAN Volume Controller disk array unit. Both procedures must be performed for this operation to be successful.

Procedure A

Procedure A applies to Tru64 UNIX version 4.0f, and later. For more information, see the Tru64 UNIX ddr.dbase and ddr_config man files.

Perform the following steps to set up the Tru64 UNIX device parameter database for features that are specific to the SAN Volume Controller:

Quiesce the storage.
Place the host system in single-user mode as root.

Edit the /etc/ddr.dbase file by including the following lines as an entry in the DISKS subsection:

SCSIDEVICE
    #
    # Values for the IBM 2145
    #
    Type = disk
    Name = "IBM" "2145"
    #
    PARAMETERS:
        TypeSubClass        = hard_disk, raid
        BadBlockRecovery    = disabled
        DynamicGeometry     = true
        LongTimeoutRetry    = enabled
        PwrMgmt_Capable     = false
        TagQueueDepth       = 20
        ReadyTimeSeconds    = 180
        CMD_WriteVerify     = supported
        InquiryLength       = 255
        RequestSenseLength  = 255

Compile the ddr.dbase file by issuing the following command:
ddr_config –c
Confirm the values by issuing the following command:
ddr_config –s disk "IBM" "2145"

Procedure B

Procedure B requires a kernel rebuild.

Perform the following steps to set a kernel SCSI parameter:

Quiesce the storage.
Place the host system in single-user mode and as root.
Edit the /sys/data/cam_data.c file by changing the non-read/write command time-out values in the changeable disk driver time-out section.
Change from u_long cdisk_to_def = 10; /* 10 seconds */ to u_long cdisk_to_def = 60; /* 60 seconds */

Compile the cam_data.c file by issuing the following command:

deconfig –c "hostname"

where hostname is the name of the system kernel which can be found in the /sys/conf/ directory.

The following example shows output from the –c "hostname" command:

#doconfig -c "ES47"
*** KERNEL CONFIGURATION AND BUILD PROCEDURE ***

Saving /sys/conf/ES47 as /sys/conf/ES47.bck

Do you want to edit the configuration file? (y/n) [n]: y

Using ed to edit the configuration file.  Press return when ready,
or type 'quit' to skip the editing session: quit


*** PERFORMING KERNEL BUILD ***
Working....Wed Mar 22 17:36:19 PST 2006

The new kernel is /sys/ES47/vmunix
#