Documentation/blockdev/cciss.txt - linux - Git at Google

 This driver is for Compaq's SMART Array Controllers.

 Supported Cards:
 ----------------

 This driver is known to work with the following cards:

 	* SA 5300
 	* SA 5i
 	* SA 532
 	* SA 5312
 	* SA 641
 	* SA 642
 	* SA 6400
 	* SA 6400 U320 Expansion Module
 	* SA 6i
 	* SA P600
 	* SA P800
 	* SA E400
 	* SA P400i
 	* SA E200
 	* SA E200i
 	* SA E500
 	* SA P700m
 	* SA P212
 	* SA P410
 	* SA P410i
 	* SA P411
 	* SA P812
 	* SA P712m
 	* SA P711m

 Detecting drive failures:
 -------------------------

 To get the status of logical volumes and to detect physical drive
 failures, you can use the cciss_vol_status program found here:
 http://cciss.sourceforge.net/#cciss_utils

 Device Naming:
 --------------

 If nodes are not already created in the /dev/cciss directory, run as root:

 # cd /dev
 # ./MAKEDEV cciss

 You need some entries in /dev for the cciss device.  The MAKEDEV script
 can make device nodes for you automatically.  Currently the device setup
 is as follows:

 Major numbers:
 	104	cciss0
 	105	cciss1
 	106	cciss2
 	105	cciss3
 	108	cciss4
 	109	cciss5
 	110	cciss6
 	111	cciss7

 Minor numbers:
         b7 b6 b5 b4 b3 b2 b1 b0
         |----+----| |----+----|
              |           |
              |           +-------- Partition ID (0=wholedev, 1-15 partition)
              |
              +-------------------- Logical Volume number

 The device naming scheme is:
 /dev/cciss/c0d0			Controller 0, disk 0, whole device
 /dev/cciss/c0d0p1		Controller 0, disk 0, partition 1
 /dev/cciss/c0d0p2		Controller 0, disk 0, partition 2
 /dev/cciss/c0d0p3		Controller 0, disk 0, partition 3

 /dev/cciss/c1d1			Controller 1, disk 1, whole device
 /dev/cciss/c1d1p1		Controller 1, disk 1, partition 1
 /dev/cciss/c1d1p2		Controller 1, disk 1, partition 2
 /dev/cciss/c1d1p3		Controller 1, disk 1, partition 3

 CCISS simple mode support
 -------------------------

 The "cciss_simple_mode=1" boot parameter may be used to prevent the driver
 from putting the controller into "performant" mode. The difference is that
 with simple mode, each command completion requires an interrupt, while with
 "performant mode" (the default, and ordinarily better performing) it is
 possible to have multiple command completions indicated by a single
 interrupt.

 SCSI tape drive and medium changer support
 ------------------------------------------

 SCSI sequential access devices and medium changer devices are supported and
 appropriate device nodes are automatically created.  (e.g.
 /dev/st0, /dev/st1, etc.  See the "st" man page for more details.)
 You must enable "SCSI tape drive support for Smart Array 5xxx" and
 "SCSI support" in your kernel configuration to be able to use SCSI
 tape drives with your Smart Array 5xxx controller.

 Additionally, note that the driver will engage the SCSI core at init
 time if any tape drives or medium changers are detected.  The driver may
 also be directed to dynamically engage the SCSI core via the /proc filesystem
 entry which the "block" side of the driver creates as
 /proc/driver/cciss/cciss* at runtime.  This is best done via a script.

 For example:

 	for x in /proc/driver/cciss/cciss[0-9]*
 	do
 		echo "engage scsi" > $x
 	done

 Once the SCSI core is engaged by the driver, it cannot be disengaged
 (except by unloading the driver, if it happens to be linked as a module.)

 Note also that if no sequential access devices or medium changers are
 detected, the SCSI core will not be engaged by the action of the above
 script.

 Hot plug support for SCSI tape drives
 -------------------------------------

 Hot plugging of SCSI tape drives is supported, with some caveats.
 The cciss driver must be informed that changes to the SCSI bus
 have been made.  This may be done via the /proc filesystem.
 For example:

 	echo "rescan" > /proc/scsi/cciss0/1

 This causes the driver to query the adapter about changes to the
 physical SCSI buses and/or fibre channel arbitrated loop and the
 driver to make note of any new or removed sequential access devices
 or medium changers.  The driver will output messages indicating what
 devices have been added or removed and the controller, bus, target and
 lun used to address the device.  It then notifies the SCSI mid layer
 of these changes.

 Note that the naming convention of the /proc filesystem entries
 contains a number in addition to the driver name.  (E.g. "cciss0"
 instead of just "cciss" which you might expect.)

 Note: ONLY sequential access devices and medium changers are presented
 as SCSI devices to the SCSI mid layer by the cciss driver.  Specifically,
 physical SCSI disk drives are NOT presented to the SCSI mid layer.  The
 physical SCSI disk drives are controlled directly by the array controller
 hardware and it is important to prevent the kernel from attempting to directly
 access these devices too, as if the array controller were merely a SCSI
 controller in the same way that we are allowing it to access SCSI tape drives.

 SCSI error handling for tape drives and medium changers
 -------------------------------------------------------

 The linux SCSI mid layer provides an error handling protocol which
 kicks into gear whenever a SCSI command fails to complete within a
 certain amount of time (which can vary depending on the command).
 The cciss driver participates in this protocol to some extent.  The
 normal protocol is a four step process.  First the device is told
 to abort the command.  If that doesn't work, the device is reset.
 If that doesn't work, the SCSI bus is reset.  If that doesn't work
 the host bus adapter is reset.  Because the cciss driver is a block
 driver as well as a SCSI driver and only the tape drives and medium
 changers are presented to the SCSI mid layer, and unlike more
 straightforward SCSI drivers, disk i/o continues through the block
 side during the SCSI error recovery process, the cciss driver only
 implements the first two of these actions, aborting the command, and
 resetting the device.  Additionally, most tape drives will not oblige
 in aborting commands, and sometimes it appears they will not even
 obey a reset command, though in most circumstances they will.  In
 the case that the command cannot be aborted and the device cannot be
 reset, the device will be set offline.

 In the event the error handling code is triggered and a tape drive is
 successfully reset or the tardy command is successfully aborted, the
 tape drive may still not allow i/o to continue until some command
 is issued which positions the tape to a known position.  Typically you
 must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
 before i/o can proceed again to a tape drive which was reset.

 There is a cciss_tape_cmds module parameter which can be used to make cciss
 allocate more commands for use by tape drives.  Ordinarily only a few commands
 (6) are allocated for tape drives because tape drives are slow and
 infrequently used and the primary purpose of Smart Array controllers is to
 act as a RAID controller for disk drives, so the vast majority of commands
 are allocated for disk devices.  However, if you have more than a few tape
 drives attached to a smart array, the default number of commands may not be
 enough (for example, if you have 8 tape drives, you could only rewind 6
 at one time with the default number of commands.)  The cciss_tape_cmds module
 parameter allows more commands (up to 16 more) to be allocated for use by
 tape drives.  For example:

         insmod cciss.ko cciss_tape_cmds=16

 Or, as a kernel boot parameter passed in via grub:  cciss.cciss_tape_cmds=8
	This driver is for Compaq's SMART Array Controllers.

	Supported Cards:
	----------------

	This driver is known to work with the following cards:

	* SA 5300
	* SA 5i
	* SA 532
	* SA 5312
	* SA 641
	* SA 642
	* SA 6400
	* SA 6400 U320 Expansion Module
	* SA 6i
	* SA P600
	* SA P800
	* SA E400
	* SA P400i
	* SA E200
	* SA E200i
	* SA E500
	* SA P700m
	* SA P212
	* SA P410
	* SA P410i
	* SA P411
	* SA P812
	* SA P712m
	* SA P711m

	Detecting drive failures:
	-------------------------

	To get the status of logical volumes and to detect physical drive
	failures, you can use the cciss_vol_status program found here:
	http://cciss.sourceforge.net/#cciss_utils

	Device Naming:
	--------------

	If nodes are not already created in the /dev/cciss directory, run as root:

	# cd /dev
	# ./MAKEDEV cciss

	You need some entries in /dev for the cciss device. The MAKEDEV script
	can make device nodes for you automatically. Currently the device setup
	is as follows:

	Major numbers:
	104 cciss0
	105 cciss1
	106 cciss2
	105 cciss3
	108 cciss4
	109 cciss5
	110 cciss6
	111 cciss7

	Minor numbers:
	b7 b6 b5 b4 b3 b2 b1 b0
	\|----+----\| \|----+----\|
	\| \|
	\| +-------- Partition ID (0=wholedev, 1-15 partition)
	\|
	+-------------------- Logical Volume number

	The device naming scheme is:
	/dev/cciss/c0d0 Controller 0, disk 0, whole device
	/dev/cciss/c0d0p1 Controller 0, disk 0, partition 1
	/dev/cciss/c0d0p2 Controller 0, disk 0, partition 2
	/dev/cciss/c0d0p3 Controller 0, disk 0, partition 3

	/dev/cciss/c1d1 Controller 1, disk 1, whole device
	/dev/cciss/c1d1p1 Controller 1, disk 1, partition 1
	/dev/cciss/c1d1p2 Controller 1, disk 1, partition 2
	/dev/cciss/c1d1p3 Controller 1, disk 1, partition 3

	CCISS simple mode support
	-------------------------

	The "cciss_simple_mode=1" boot parameter may be used to prevent the driver
	from putting the controller into "performant" mode. The difference is that
	with simple mode, each command completion requires an interrupt, while with
	"performant mode" (the default, and ordinarily better performing) it is
	possible to have multiple command completions indicated by a single
	interrupt.

	SCSI tape drive and medium changer support
	------------------------------------------

	SCSI sequential access devices and medium changer devices are supported and
	appropriate device nodes are automatically created. (e.g.
	/dev/st0, /dev/st1, etc. See the "st" man page for more details.)
	You must enable "SCSI tape drive support for Smart Array 5xxx" and
	"SCSI support" in your kernel configuration to be able to use SCSI
	tape drives with your Smart Array 5xxx controller.

	Additionally, note that the driver will engage the SCSI core at init
	time if any tape drives or medium changers are detected. The driver may
	also be directed to dynamically engage the SCSI core via the /proc filesystem
	entry which the "block" side of the driver creates as
	/proc/driver/cciss/cciss* at runtime. This is best done via a script.

	For example:

	for x in /proc/driver/cciss/cciss[0-9]*
	do
	echo "engage scsi" > $x
	done

	Once the SCSI core is engaged by the driver, it cannot be disengaged
	(except by unloading the driver, if it happens to be linked as a module.)

	Note also that if no sequential access devices or medium changers are
	detected, the SCSI core will not be engaged by the action of the above
	script.

	Hot plug support for SCSI tape drives
	-------------------------------------

	Hot plugging of SCSI tape drives is supported, with some caveats.
	The cciss driver must be informed that changes to the SCSI bus
	have been made. This may be done via the /proc filesystem.
	For example:

	echo "rescan" > /proc/scsi/cciss0/1

	This causes the driver to query the adapter about changes to the
	physical SCSI buses and/or fibre channel arbitrated loop and the
	driver to make note of any new or removed sequential access devices
	or medium changers. The driver will output messages indicating what
	devices have been added or removed and the controller, bus, target and
	lun used to address the device. It then notifies the SCSI mid layer
	of these changes.

	Note that the naming convention of the /proc filesystem entries
	contains a number in addition to the driver name. (E.g. "cciss0"
	instead of just "cciss" which you might expect.)

	Note: ONLY sequential access devices and medium changers are presented
	as SCSI devices to the SCSI mid layer by the cciss driver. Specifically,
	physical SCSI disk drives are NOT presented to the SCSI mid layer. The
	physical SCSI disk drives are controlled directly by the array controller
	hardware and it is important to prevent the kernel from attempting to directly
	access these devices too, as if the array controller were merely a SCSI
	controller in the same way that we are allowing it to access SCSI tape drives.

	SCSI error handling for tape drives and medium changers
	-------------------------------------------------------

	The linux SCSI mid layer provides an error handling protocol which
	kicks into gear whenever a SCSI command fails to complete within a
	certain amount of time (which can vary depending on the command).
	The cciss driver participates in this protocol to some extent. The
	normal protocol is a four step process. First the device is told
	to abort the command. If that doesn't work, the device is reset.
	If that doesn't work, the SCSI bus is reset. If that doesn't work
	the host bus adapter is reset. Because the cciss driver is a block
	driver as well as a SCSI driver and only the tape drives and medium
	changers are presented to the SCSI mid layer, and unlike more
	straightforward SCSI drivers, disk i/o continues through the block
	side during the SCSI error recovery process, the cciss driver only
	implements the first two of these actions, aborting the command, and
	resetting the device. Additionally, most tape drives will not oblige
	in aborting commands, and sometimes it appears they will not even
	obey a reset command, though in most circumstances they will. In
	the case that the command cannot be aborted and the device cannot be
	reset, the device will be set offline.

	In the event the error handling code is triggered and a tape drive is
	successfully reset or the tardy command is successfully aborted, the
	tape drive may still not allow i/o to continue until some command
	is issued which positions the tape to a known position. Typically you
	must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
	before i/o can proceed again to a tape drive which was reset.

	There is a cciss_tape_cmds module parameter which can be used to make cciss
	allocate more commands for use by tape drives. Ordinarily only a few commands
	(6) are allocated for tape drives because tape drives are slow and
	infrequently used and the primary purpose of Smart Array controllers is to
	act as a RAID controller for disk drives, so the vast majority of commands
	are allocated for disk devices. However, if you have more than a few tape
	drives attached to a smart array, the default number of commands may not be
	enough (for example, if you have 8 tape drives, you could only rewind 6
	at one time with the default number of commands.) The cciss_tape_cmds module
	parameter allows more commands (up to 16 more) to be allocated for use by
	tape drives. For example:

	insmod cciss.ko cciss_tape_cmds=16

	Or, as a kernel boot parameter passed in via grub: cciss.cciss_tape_cmds=8