[linux-2.6-block.git] / Documentation / cciss.txt

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

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

# cd /dev
# ./MAKEDEV cciss

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

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

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 not engage the SCSI core at init 
time.  The driver must 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 because at driver init time, 
the SCSI core may not yet be initialized (because the driver is a block 
driver) and attempting to register it with the SCSI core in such a case 
would cause a hang.  This is best done via an initialization script 
(typically in /etc/init.d, but could vary depending on distibution). 
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, in addition to and prior to informing the SCSI 
mid layer.  This may be done via the /proc filesystem.  For example:

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

This causes the adapter 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.  Once this is done, the SCSI mid layer 
can be informed of changes to the virtual SCSI bus which the driver 
presents to it in the usual way. For example: 

	echo scsi add-single-device 3 2 1 0 > /proc/scsi/scsi
 
to add a device on controller 3, bus 2, target 1, lun 0.   Note that
the driver makes an effort to preserve the devices positions
in the virtual SCSI bus, so if you are only moving tape drives 
around on the same adapter and not adding or removing tape drives 
from the adapter, informing the SCSI mid layer may not be necessary.

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 coommand, 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.
Commit	Line	Data
1da177e4 LT	1	This driver is for Compaq's SMART Array Controllers.
	2
	3	Supported Cards:
	4	----------------
	5
	6	This driver is known to work with the following cards:
	7
	8	* SA 5300
	9	* SA 5i
	10	* SA 532
	11	* SA 5312
	12	* SA 641
	13	* SA 642
	14	* SA 6400
	15	* SA 6400 U320 Expansion Module
	16	* SA 6i
	17	* SA P600
	18	* SA P800
	19	* SA E400
9dc7a86e MM	20	* SA P400i
	21	* SA E200
	22	* SA E200i
1da177e4 LT	23
	24	If nodes are not already created in the /dev/cciss directory, run as root:
	25
	26	# cd /dev
	27	# ./MAKEDEV cciss
	28
	29	Device Naming:
	30	--------------
	31
	32	You need some entries in /dev for the cciss device. The MAKEDEV script
	33	can make device nodes for you automatically. Currently the device setup
	34	is as follows:
	35
	36	Major numbers:
	37	104 cciss0
	38	105 cciss1
	39	106 cciss2
	40	105 cciss3
	41	108 cciss4
	42	109 cciss5
	43	110 cciss6
	44	111 cciss7
	45
	46	Minor numbers:
	47	b7 b6 b5 b4 b3 b2 b1 b0
	48	\|----+----\| \|----+----\|
	49	\| \|
	50	\| +-------- Partition ID (0=wholedev, 1-15 partition)
	51	\|
	52	+-------------------- Logical Volume number
	53
	54	The device naming scheme is:
	55	/dev/cciss/c0d0 Controller 0, disk 0, whole device
	56	/dev/cciss/c0d0p1 Controller 0, disk 0, partition 1
	57	/dev/cciss/c0d0p2 Controller 0, disk 0, partition 2
	58	/dev/cciss/c0d0p3 Controller 0, disk 0, partition 3
	59
	60	/dev/cciss/c1d1 Controller 1, disk 1, whole device
	61	/dev/cciss/c1d1p1 Controller 1, disk 1, partition 1
	62	/dev/cciss/c1d1p2 Controller 1, disk 1, partition 2
	63	/dev/cciss/c1d1p3 Controller 1, disk 1, partition 3
	64
	65	SCSI tape drive and medium changer support
	66	------------------------------------------
	67
	68	SCSI sequential access devices and medium changer devices are supported and
	69	appropriate device nodes are automatically created. (e.g.
	70	/dev/st0, /dev/st1, etc. See the "st" man page for more details.)
	71	You must enable "SCSI tape drive support for Smart Array 5xxx" and
	72	"SCSI support" in your kernel configuration to be able to use SCSI
	73	tape drives with your Smart Array 5xxx controller.
	74
	75	Additionally, note that the driver will not engage the SCSI core at init
	76	time. The driver must be directed to dynamically engage the SCSI core via
	77	the /proc filesystem entry which the "block" side of the driver creates as
	78	/proc/driver/cciss/cciss* at runtime. This is because at driver init time,
	79	the SCSI core may not yet be initialized (because the driver is a block
	80	driver) and attempting to register it with the SCSI core in such a case
	81	would cause a hang. This is best done via an initialization script
	82	(typically in /etc/init.d, but could vary depending on distibution).
	83	For example:
	84
	85	for x in /proc/driver/cciss/cciss[0-9]*
	86	do
87	echo "engage scsi" > $x
88	done
89
90	Once the SCSI core is engaged by the driver, it cannot be disengaged
91	(except by unloading the driver, if it happens to be linked as a module.)
92
93	Note also that if no sequential access devices or medium changers are
94	detected, the SCSI core will not be engaged by the action of the above
95	script.
96
97	Hot plug support for SCSI tape drives
98	-------------------------------------
99
100	Hot plugging of SCSI tape drives is supported, with some caveats.
101	The cciss driver must be informed that changes to the SCSI bus
102	have been made, in addition to and prior to informing the SCSI
103	mid layer. This may be done via the /proc filesystem. For example:
104
105	echo "rescan" > /proc/scsi/cciss0/1
106
107	This causes the adapter to query the adapter about changes to the
108	physical SCSI buses and/or fibre channel arbitrated loop and the
109	driver to make note of any new or removed sequential access devices
110	or medium changers. The driver will output messages indicating what
111	devices have been added or removed and the controller, bus, target and
112	lun used to address the device. Once this is done, the SCSI mid layer
113	can be informed of changes to the virtual SCSI bus which the driver
114	presents to it in the usual way. For example:
115
116	echo scsi add-single-device 3 2 1 0 > /proc/scsi/scsi
117
118	to add a device on controller 3, bus 2, target 1, lun 0. Note that
119	the driver makes an effort to preserve the devices positions
120	in the virtual SCSI bus, so if you are only moving tape drives
121	around on the same adapter and not adding or removing tape drives
122	from the adapter, informing the SCSI mid layer may not be necessary.
123
124	Note that the naming convention of the /proc filesystem entries
125	contains a number in addition to the driver name. (E.g. "cciss0"
126	instead of just "cciss" which you might expect.)
127
128	Note: ONLY sequential access devices and medium changers are presented
129	as SCSI devices to the SCSI mid layer by the cciss driver. Specifically,
130	physical SCSI disk drives are NOT presented to the SCSI mid layer. The
131	physical SCSI disk drives are controlled directly by the array controller
132	hardware and it is important to prevent the kernel from attempting to directly
133	access these devices too, as if the array controller were merely a SCSI
134	controller in the same way that we are allowing it to access SCSI tape drives.
135
3da8b713	136	SCSI error handling for tape drives and medium changers
	137	-------------------------------------------------------
	138
	139	The linux SCSI mid layer provides an error handling protocol which
	140	kicks into gear whenever a SCSI command fails to complete within a
	141	certain amount of time (which can vary depending on the command).
	142	The cciss driver participates in this protocol to some extent. The
	143	normal protocol is a four step process. First the device is told
	144	to abort the command. If that doesn't work, the device is reset.
	145	If that doesn't work, the SCSI bus is reset. If that doesn't work
	146	the host bus adapter is reset. Because the cciss driver is a block
	147	driver as well as a SCSI driver and only the tape drives and medium
	148	changers are presented to the SCSI mid layer, and unlike more
	149	straightforward SCSI drivers, disk i/o continues through the block
	150	side during the SCSI error recovery process, the cciss driver only
	151	implements the first two of these actions, aborting the command, and
	152	resetting the device. Additionally, most tape drives will not oblige
	153	in aborting commands, and sometimes it appears they will not even
	154	obey a reset coommand, though in most circumstances they will. In
	155	the case that the command cannot be aborted and the device cannot be
	156	reset, the device will be set offline.
	157
	158	In the event the error handling code is triggered and a tape drive is
	159	successfully reset or the tardy command is successfully aborted, the
	160	tape drive may still not allow i/o to continue until some command
	161	is issued which positions the tape to a known position. Typically you
	162	must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
	163	before i/o can proceed again to a tape drive which was reset.
	164