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drd_dma(8)


NAME

  drd_dma - Determines if the use of peer-to-peer direct memory access (DMA)
  in the distributed raw disk (DRD) subsystem can be used to enhance cluster
  performance, and optionally enables it (provided on Production Server
  configurations only)


SYNOPSIS

  /usr/sbin/drd_dma [flags]


FLAGS

  -h	    Returns usage information.

  -o	    Prevents the drd_dma utility from failing if it encounters an
	    unknown CPU or bus type.

  -p	    Enables peer-to-peer DMA if the drd_dma utility determines that
	    doing so will enhance DRD subsystem performance. If the
	    configuration variable TCR_DRD_PEER2PEER is set in the
	    /etc/rc.config file when you invoke the drd_dma utility with this
	    flag, the utility returns an error.

  -v	    Displays details about the member system's Memory Channel and
	    SCSI bus configuration and the reasons, if any, why it cannot
	    enable peer-to-peer DMA.


DESCRIPTION

  The drd_dma utility determines if the use of peer-to-peer DMA in the DRD
  subsystem will enhance cluster performance, and optionally enables it.  The
  utility runs at boot time on each member system and examines its hardware
  configuration. It enables peer-to-peer DMA if it is safe to do so, and if
  the drd-bss-rm-peer2peer kernel attribute has not been explicitly set to 0
  (zero) in the /etc/sysconfigtab file.

  When enabled on a cluster member system, peer-to-peer DMA is used for all
  remote DRD read requests processed by that member system as a DRD server.
  Data read in response to the request is sent directly to the Memory Channel
  adapter from the disk controller. This avoids an intermediate transfer by
  way of main memory and diminishes the CPU load of the DRD server.

				     Note
       Although peer-to-peer DMA can be used when reading from a disk to the
       Memory Channel adapter, it cannot be used when writing to a disk from
       the Memory Channel due to current hardware limitations.

  For a DRD server to use peer-to-peer DMA, all SCSI controllers and Memory
  Channel adapters used by DRD must be on the same PCI bus. The drd_dma
  utility checks for valid configurations, and returns a message indicating
  whether peer-to-peer DMA can or cannot be enabled. It displays another
  message if peer-to-peer DMA is already enabled. If you specify the -p flag
  and the member system is able to use peer-to-peer DMA, the drd_dma utility
  will automatically enable it.

  In some instances, the drd_dma utility cannot unequivocally determine that
  a configuration can support peer-to-peer DMA, returning a message stating
  that peer-to-peer DMA cannot be enabled. For example, a member system may
  have multiple PCI buses with SCSI controllers attached to each. As long as
  the DRD disks on which a given DRD server relies are on the same PCI bus as
  all Memory Channel adapters, you can safely enable peer-to-peer DMA on that
  member system. To do so, you must manually set the drd-bss-rm-peer2peer
  kernel attribute to a nonzero value using the sysconfig command, as
  directed in the drd(7) reference page. You must ensure that no DRD disks
  are active at the time you enter this command. If DRD disks are active at
  the time you enter the command, the system may panic.

  Finally, if the drd-data-compare parameter is enabled at the time the
  drd_dma utility attempts to enable peer-to-peer DMA, the following error is
  returned:

       Cannot configure drd-bss-rm-peer2peer when drd-data-compare is enabled

  The drd-bss-rm-peer2peer and drd-data-compare parameters are incompatible.
  To enable peer-to-peer DMA, you must ensure that the drd-data-compare
  parameter is set to 0 (zero), its default value.  See the drd(7) reference
  page for more information.


EXAMPLES

  The following example shows the output of a drd_dma command:

       % /usr/sbin/drd_dma

	 /usr/sbin/drd_dma: Peer-to-peer DMA is sure to work between
		      scsi and Memory Channel controllers
	 /usr/sbin/drd_dma: Peer-to-peer DMA over Memory Channel is enabled.

  The following example shows the output of a drd_dma command when used with
  the -v flag on a member system that has not been configured properly to use
  peer-to-peer DMA:

       % /usr/sbin/drd_dma -v

       Root device is mounted on LSM
       No peer to peer DMA, because 'psiop' is a scsi bus driver without cluster
       support
       Memory Channel Controllers: 1
       Cluster scsi   Controllers: 1
       There is 1 configuration problem making peer to peer DMA over MC impossible
       /usr/sbin/drd_dma: Peer-to-peer DMA is NOT sure to work between
				scsi and Memory Channel controllers
       /usr/sbin/drd_dma: Peer-to-peer DMA over Memory Channel is NOT enabled.


FILE

  /usr/sbin/drd_dma
	    Specifies the command path.


RELATED INFORMATION

  drd(7), asemgr(8), drd_balance(8), drd_ivp(8), drd_mknod(8)

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