Root/Documentation/blockdev/cciss.txt

1This driver is for Compaq's SMART Array Controllers.
2
3Supported Cards:
4----------------
5
6This 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
20    * SA P400i
21    * SA E200
22    * SA E200i
23    * SA E500
24    * SA P700m
25    * SA P212
26    * SA P410
27    * SA P410i
28    * SA P411
29    * SA P812
30    * SA P712m
31    * SA P711m
32
33Detecting drive failures:
34-------------------------
35
36To get the status of logical volumes and to detect physical drive
37failures, you can use the cciss_vol_status program found here:
38http://cciss.sourceforge.net/#cciss_utils
39
40Device Naming:
41--------------
42
43If nodes are not already created in the /dev/cciss directory, run as root:
44
45# cd /dev
46# ./MAKEDEV cciss
47
48You need some entries in /dev for the cciss device. The MAKEDEV script
49can make device nodes for you automatically. Currently the device setup
50is as follows:
51
52Major numbers:
53    104 cciss0
54    105 cciss1
55    106 cciss2
56    105 cciss3
57    108 cciss4
58    109 cciss5
59    110 cciss6
60    111 cciss7
61
62Minor numbers:
63        b7 b6 b5 b4 b3 b2 b1 b0
64        |----+----| |----+----|
65             | |
66             | +-------- Partition ID (0=wholedev, 1-15 partition)
67             |
68             +-------------------- Logical Volume number
69
70The device naming scheme is:
71/dev/cciss/c0d0 Controller 0, disk 0, whole device
72/dev/cciss/c0d0p1 Controller 0, disk 0, partition 1
73/dev/cciss/c0d0p2 Controller 0, disk 0, partition 2
74/dev/cciss/c0d0p3 Controller 0, disk 0, partition 3
75
76/dev/cciss/c1d1 Controller 1, disk 1, whole device
77/dev/cciss/c1d1p1 Controller 1, disk 1, partition 1
78/dev/cciss/c1d1p2 Controller 1, disk 1, partition 2
79/dev/cciss/c1d1p3 Controller 1, disk 1, partition 3
80
81SCSI tape drive and medium changer support
82------------------------------------------
83
84SCSI sequential access devices and medium changer devices are supported and
85appropriate device nodes are automatically created. (e.g.
86/dev/st0, /dev/st1, etc. See the "st" man page for more details.)
87You must enable "SCSI tape drive support for Smart Array 5xxx" and
88"SCSI support" in your kernel configuration to be able to use SCSI
89tape drives with your Smart Array 5xxx controller.
90
91Additionally, note that the driver will not engage the SCSI core at init
92time. The driver must be directed to dynamically engage the SCSI core via
93the /proc filesystem entry which the "block" side of the driver creates as
94/proc/driver/cciss/cciss* at runtime. This is because at driver init time,
95the SCSI core may not yet be initialized (because the driver is a block
96driver) and attempting to register it with the SCSI core in such a case
97would cause a hang. This is best done via an initialization script
98(typically in /etc/init.d, but could vary depending on distribution).
99For example:
100
101    for x in /proc/driver/cciss/cciss[0-9]*
102    do
103        echo "engage scsi" > $x
104    done
105
106Once the SCSI core is engaged by the driver, it cannot be disengaged
107(except by unloading the driver, if it happens to be linked as a module.)
108
109Note also that if no sequential access devices or medium changers are
110detected, the SCSI core will not be engaged by the action of the above
111script.
112
113Hot plug support for SCSI tape drives
114-------------------------------------
115
116Hot plugging of SCSI tape drives is supported, with some caveats.
117The cciss driver must be informed that changes to the SCSI bus
118have been made. This may be done via the /proc filesystem.
119For example:
120
121    echo "rescan" > /proc/scsi/cciss0/1
122
123This causes the driver to query the adapter about changes to the
124physical SCSI buses and/or fibre channel arbitrated loop and the
125driver to make note of any new or removed sequential access devices
126or medium changers. The driver will output messages indicating what
127devices have been added or removed and the controller, bus, target and
128lun used to address the device. It then notifies the SCSI mid layer
129of these changes.
130
131Note that the naming convention of the /proc filesystem entries
132contains a number in addition to the driver name. (E.g. "cciss0"
133instead of just "cciss" which you might expect.)
134
135Note: ONLY sequential access devices and medium changers are presented
136as SCSI devices to the SCSI mid layer by the cciss driver. Specifically,
137physical SCSI disk drives are NOT presented to the SCSI mid layer. The
138physical SCSI disk drives are controlled directly by the array controller
139hardware and it is important to prevent the kernel from attempting to directly
140access these devices too, as if the array controller were merely a SCSI
141controller in the same way that we are allowing it to access SCSI tape drives.
142
143SCSI error handling for tape drives and medium changers
144-------------------------------------------------------
145
146The linux SCSI mid layer provides an error handling protocol which
147kicks into gear whenever a SCSI command fails to complete within a
148certain amount of time (which can vary depending on the command).
149The cciss driver participates in this protocol to some extent. The
150normal protocol is a four step process. First the device is told
151to abort the command. If that doesn't work, the device is reset.
152If that doesn't work, the SCSI bus is reset. If that doesn't work
153the host bus adapter is reset. Because the cciss driver is a block
154driver as well as a SCSI driver and only the tape drives and medium
155changers are presented to the SCSI mid layer, and unlike more
156straightforward SCSI drivers, disk i/o continues through the block
157side during the SCSI error recovery process, the cciss driver only
158implements the first two of these actions, aborting the command, and
159resetting the device. Additionally, most tape drives will not oblige
160in aborting commands, and sometimes it appears they will not even
161obey a reset command, though in most circumstances they will. In
162the case that the command cannot be aborted and the device cannot be
163reset, the device will be set offline.
164
165In the event the error handling code is triggered and a tape drive is
166successfully reset or the tardy command is successfully aborted, the
167tape drive may still not allow i/o to continue until some command
168is issued which positions the tape to a known position. Typically you
169must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
170before i/o can proceed again to a tape drive which was reset.
171
172There is a cciss_tape_cmds module parameter which can be used to make cciss
173allocate more commands for use by tape drives. Ordinarily only a few commands
174(6) are allocated for tape drives because tape drives are slow and
175infrequently used and the primary purpose of Smart Array controllers is to
176act as a RAID controller for disk drives, so the vast majority of commands
177are allocated for disk devices. However, if you have more than a few tape
178drives attached to a smart array, the default number of commands may not be
179enought (for example, if you have 8 tape drives, you could only rewind 6
180at one time with the default number of commands.) The cciss_tape_cmds module
181parameter allows more commands (up to 16 more) to be allocated for use by
182tape drives. For example:
183
184        insmod cciss.ko cciss_tape_cmds=16
185
186Or, as a kernel boot parameter passed in via grub: cciss.cciss_tape_cmds=8
187

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