NAME

dcc − control read and write caching for HP SCSI disk array drives

SYNOPSIS

dcc [options] [drive_list] device_file

DESCRIPTION

dcc displays or changes the read-ahead caching status, and write-immediate reporting status of selected drives on the HP SCSI disk array referenced by device_file.

Options

-d Display only.  Displays the read-ahead caching and write immediate reporting status of all selected drives on the HP SCSI disk array.  For HP C2430 disk array devices, the number and size of cache segments is displayed.  This option cannot be used with any other option. 

-ron Read on.  Enables read-ahead caching on all selected drives of the HP SCSI disk array.  Can be used in combination with one of the write-immediate reporting options. 

-roff Read off.  Disables read-ahead caching on all selected drives of the HP SCSI disk array.  Can be used in combination with one of the write-immediate reporting options. 

-won Write on.  Enables write-immediate reporting on all selected drives of the HP SCSI disk array.  Can be used in combination with one of the read-ahead caching options. 

-woff Write off.  Disables write immediate reporting on all selected drives of the HP SCSI disk array.  Can be used in combination with one of the read-ahead caching options. 

-snum_segments Set the number of cache segments.  This option is unique to the HP C2430 disk array.  The disk mechanism cache can be segmented into 1, 2, 4, 8 or 16 segments.  The default is 2 segments.  This option cannot be used with other options. 

drive_list Specify a set of drives.  If this optional list is absent, the default set of affected drives is all drives attached to the controller.  The list is in the form cXiY ,... where X (a decimal number) represents SCSI channel number, and Y (a decimal number) represents the SCSI ID of the drive.  Multiple drives in the list are separated by commas. 

RETURN VALUE

dcc returns the following values:

0 Successful completion. 

-1 Command failed (an error occurred). 

ERROR MESSAGES

Errors can originate from problems with:

• dcc

• SCSI (device level) communications

• system calls

Error messages generated by dcc:

usage: dcc options [cXiY,...] <special>
An error in command syntax has occurred. Enter command again with the required arguments, in the order shown.

dcc: Arg out of range
One of the arguments is larger than its allowed maximum value (or smaller than its allowed minimum value), or is incorrect in form.  Check the size, and form of each argument and make appropriate corrections.

dcc: device busy
To ensure that dcc does not modify a disk array that is being used by another process, dcc attempts to obtain exclusive access to the disk array.  If the disk array is already opened by another process (for example, LVM — the Logical Volume Manager), a "device busy" error message is returned by the driver.  To eliminate the "device busy" condition, determine what process has the device open.  In the case of LVM, it is necessary to deactivate the volume group containing the array before configuring the array (see vgchange(1M)). 

dcc: LUN does not exist
The addressed LUN is not known to the array controller. 

dcc: LUN # too big
The LUN number, which is derived from the device special file name, is out of range. 

dcc: Not a raw file
Utilities must be able to open the device file for raw access.

dcc: Not an HP SCSI disk array
The device is not an HP SCSI disk array. 

dcc: Transfer length error
The amount of data actually sent to (or received from) the device was not the expected amount.

SCSI (device level) communication errors:

Sense data associated with the failed operation is printed. 

Error messages generated by system calls:

dcc uses the following system calls:

malloc(), free(), stat(), open(), close(), read(), write(), and ioctl(). 

Documentation for these HP-UX system calls contains information about the specific error conditions associated with each call.  dcc does not alter the value of errno.  The interpretation of errno for printing purposes is performed by the system utility strerror(). 

EXAMPLES

To display the status of read and write caching on all the drives of the disk array /dev/rdsk/c2t2d0 on a Series 700:

dcc -d /dev/rdsk/c2t2d0

To enable write-immediate reporting on a list of drives on the disk array /dev/rdsk/c2t2d0 on a Series 800:

dcc -won c2i0,c1i0,c5i0,c4i1 /dev/rdsk/c2t2d0

To disable read caching and write-immediate reporting on the drives of the disk array /dev/rdsk/c2t4d0 on a Series 700:

dcc -roff -woff /dev/rdsk/c2t4d0

To set the number of cache segments on the HP C2430 disk array /dev/rdsk/c2t2d0 to 4 on a Series 800:

dcc -s 4 /dev/rdsk/c2t2d0

DEPENDENCIES

The HP C2425 and HP C2427 disk arrays are only supported on Series 700 systems running HP-UX version 9.0X. 

The HP C2430 disk array is supported on Series 700 and 800 systems runing HP-UX versions 9.0X and 10.0X. 

AUTHOR

dcc was developed by HP. 

Hewlett-Packard Company  —  HP-UX Release 10.20:  July 1996