Device nodes

The device naming scheme 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

Files in /proc

The files /proc/driver/cciss/cciss[0-9]+ contain information about the configuration of each controller. For example:

$ cd /proc/driver/cciss
$ ls -l
total 0
-rw-r--r-- 1 root root 0 2010-09-10 10:38 cciss0
-rw-r--r-- 1 root root 0 2010-09-10 10:38 cciss1
-rw-r--r-- 1 root root 0 2010-09-10 10:38 cciss2
$ cat cciss2
cciss2: HP Smart Array P800 Controller
Board ID: 0x3223103c
Firmware Version: 7.14
IRQ: 16
Logical drives: 1
Current Q depth: 0
Current # commands on controller: 0
Max Q depth since init: 1
Max # commands on controller since init: 2
Max SG entries since init: 32
Sequential access devices: 0
cciss/c2d0:   36.38GB       RAID 0

Files in /sys

/sys/bus/pci/devices/dev/ccissX/cXdY/model

Displays the SCSI INQUIRY page 0 model for logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/rev

Displays the SCSI INQUIRY page 0 revision for logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/unique_id

Displays the SCSI INQUIRY page 83 serial number for logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/vendor

Displays the SCSI INQUIRY page 0 vendor for logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/block:cciss!cXdY

A symbolic link to /sys/block/cciss!cXdY.

/sys/bus/pci/devices/dev/ccissX/rescan

When this file is written to, the driver rescans the controller to discover any new, removed, or modified logical drives.

/sys/bus/pci/devices/dev/ccissX/resettable

A value of 1 displayed in this file indicates that the "reset_devices=1" kernel parameter (used by kdump) is honored by this controller. A value of 0 indicates that the "reset_devices=1" kernel parameter will not be honored. Some models of Smart Array are not able to honor this parameter.

/sys/bus/pci/devices/dev/ccissX/cXdY/lunid

Displays the 8-byte LUN ID used to address logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/raid_level

Displays the RAID level of logical drive Y of controller X.

/sys/bus/pci/devices/dev/ccissX/cXdY/usage_count

Displays the usage count (number of opens) of logical drive Y of controller X.

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 st(4) 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 run time. 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 distribution). 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:

1. query the adapter about changes to the physical SCSI buses and/or fiber channel arbitrated loop, and

2. make note of any new or removed sequential access devices or medium changers.

The driver will output messages indicating which devices have been added or removed and the controller, bus, target, and lun used to address each device. The driver then notifies the SCSI midlayer 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 midlayer by the cciss driver. Specifically, physical SCSI disk drives are not presented to the SCSI midlayer. The only disk devices that are presented to the kernel are logical drives that the array controller constructs from regions on the physical drives. The logical drives are presented to the block layer (not to the SCSI midlayer). It is important for the driver to prevent the kernel from accessing the physical drives directly, since these drives are used by the array controller to construct the logical drives.

SCSI error handling for tape drives and medium changers

The Linux SCSI midlayer provides an error-handling protocol that is initiated 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:

1. First, the device is told to abort the command.

2. If that doesn't work, the device is reset.

3. If that doesn't work, the SCSI bus is reset.

4. If that doesn't work, the host bus adapter is reset.

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 midlayer. Furthermore, unlike more straightforward SCSI drivers, disk I/O continues through the block side during the SCSI error-recovery process. Therefore, the cciss driver implements only the first two of these actions, aborting the command, and resetting the device. Note also that 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. If the command cannot be aborted and the device cannot be reset, the device will be set offline.

In the event that 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 that 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 that was reset.