linux/Documentation/blockdev/cciss.txt
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   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
  81CCISS simple mode support
  82-------------------------
  83
  84The "cciss_simple_mode=1" boot parameter may be used to prevent the driver
  85from putting the controller into "performant" mode. The difference is that
  86with simple mode, each command completion requires an interrupt, while with
  87"performant mode" (the default, and ordinarily better performing) it is
  88possible to have multiple command completions indicated by a single
  89interrupt.
  90
  91SCSI tape drive and medium changer support
  92------------------------------------------
  93
  94SCSI sequential access devices and medium changer devices are supported and 
  95appropriate device nodes are automatically created.  (e.g.  
  96/dev/st0, /dev/st1, etc.  See the "st" man page for more details.) 
  97You must enable "SCSI tape drive support for Smart Array 5xxx" and 
  98"SCSI support" in your kernel configuration to be able to use SCSI
  99tape drives with your Smart Array 5xxx controller.
 100
 101Additionally, note that the driver will engage the SCSI core at init
 102time if any tape drives or medium changers are detected.  The driver may
 103also be directed to dynamically engage the SCSI core via the /proc filesystem
 104entry which the "block" side of the driver creates as
 105/proc/driver/cciss/cciss* at runtime.  This is best done via a script.
 106
 107For example:
 108
 109        for x in /proc/driver/cciss/cciss[0-9]*
 110        do
 111                echo "engage scsi" > $x
 112        done
 113
 114Once the SCSI core is engaged by the driver, it cannot be disengaged 
 115(except by unloading the driver, if it happens to be linked as a module.)
 116
 117Note also that if no sequential access devices or medium changers are
 118detected, the SCSI core will not be engaged by the action of the above
 119script.
 120
 121Hot plug support for SCSI tape drives
 122-------------------------------------
 123
 124Hot plugging of SCSI tape drives is supported, with some caveats.
 125The cciss driver must be informed that changes to the SCSI bus
 126have been made.  This may be done via the /proc filesystem.
 127For example:
 128
 129        echo "rescan" > /proc/scsi/cciss0/1
 130
 131This causes the driver to query the adapter about changes to the
 132physical SCSI buses and/or fibre channel arbitrated loop and the
 133driver to make note of any new or removed sequential access devices
 134or medium changers.  The driver will output messages indicating what 
 135devices have been added or removed and the controller, bus, target and 
 136lun used to address the device.  It then notifies the SCSI mid layer
 137of these changes.
 138
 139Note that the naming convention of the /proc filesystem entries 
 140contains a number in addition to the driver name.  (E.g. "cciss0" 
 141instead of just "cciss" which you might expect.)
 142
 143Note: ONLY sequential access devices and medium changers are presented 
 144as SCSI devices to the SCSI mid layer by the cciss driver.  Specifically, 
 145physical SCSI disk drives are NOT presented to the SCSI mid layer.  The 
 146physical SCSI disk drives are controlled directly by the array controller 
 147hardware and it is important to prevent the kernel from attempting to directly
 148access these devices too, as if the array controller were merely a SCSI 
 149controller in the same way that we are allowing it to access SCSI tape drives.
 150
 151SCSI error handling for tape drives and medium changers
 152-------------------------------------------------------
 153
 154The linux SCSI mid layer provides an error handling protocol which
 155kicks into gear whenever a SCSI command fails to complete within a
 156certain amount of time (which can vary depending on the command).
 157The cciss driver participates in this protocol to some extent.  The
 158normal protocol is a four step process.  First the device is told
 159to abort the command.  If that doesn't work, the device is reset.
 160If that doesn't work, the SCSI bus is reset.  If that doesn't work
 161the host bus adapter is reset.  Because the cciss driver is a block
 162driver as well as a SCSI driver and only the tape drives and medium
 163changers are presented to the SCSI mid layer, and unlike more 
 164straightforward SCSI drivers, disk i/o continues through the block
 165side during the SCSI error recovery process, the cciss driver only
 166implements the first two of these actions, aborting the command, and
 167resetting the device.  Additionally, most tape drives will not oblige 
 168in aborting commands, and sometimes it appears they will not even 
 169obey a reset command, though in most circumstances they will.  In
 170the case that the command cannot be aborted and the device cannot be 
 171reset, the device will be set offline.
 172
 173In the event the error handling code is triggered and a tape drive is
 174successfully reset or the tardy command is successfully aborted, the 
 175tape drive may still not allow i/o to continue until some command
 176is issued which positions the tape to a known position.  Typically you
 177must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
 178before i/o can proceed again to a tape drive which was reset.
 179
 180There is a cciss_tape_cmds module parameter which can be used to make cciss
 181allocate more commands for use by tape drives.  Ordinarily only a few commands
 182(6) are allocated for tape drives because tape drives are slow and
 183infrequently used and the primary purpose of Smart Array controllers is to
 184act as a RAID controller for disk drives, so the vast majority of commands
 185are allocated for disk devices.  However, if you have more than a few tape
 186drives attached to a smart array, the default number of commands may not be
 187enought (for example, if you have 8 tape drives, you could only rewind 6
 188at one time with the default number of commands.)  The cciss_tape_cmds module
 189parameter allows more commands (up to 16 more) to be allocated for use by
 190tape drives.  For example:
 191
 192        insmod cciss.ko cciss_tape_cmds=16
 193
 194Or, as a kernel boot parameter passed in via grub:  cciss.cciss_tape_cmds=8
 195
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