0007a4c90a
A long time ago, probably in 2002, one of the distros, or maybe more than one, loaded block drivers prior to loading the SCSI mid layer. This meant that the cciss driver, being a block driver, could not engage the SCSI mid layer at init time without panicking, and relied on being poked by a userland program after the system was up (and the SCSI mid layer was therefore present) to engage the SCSI mid layer. This is no longer the case, and cciss can safely rely on the SCSI mid layer being present at init time and engage the SCSI mid layer straight away. This means that users will see their tape drives and medium changers at driver load time without need for a script in /etc/rc.d that does this: for x in /proc/driver/cciss/cciss* do echo "engage scsi" > $x done However, if no tape drives or medium changers are detected, the SCSI mid layer will not be engaged. If a tape drive or medium change is later hot-added to the system it will then be necessary to use the above script or similar for the device(s) to be acceesible. Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
195 lines
7.3 KiB
Plaintext
195 lines
7.3 KiB
Plaintext
This driver is for Compaq's SMART Array Controllers.
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Supported Cards:
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----------------
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This driver is known to work with the following cards:
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* SA 5300
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* SA 5i
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* SA 532
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* SA 5312
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* SA 641
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* SA 642
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* SA 6400
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* SA 6400 U320 Expansion Module
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* SA 6i
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* SA P600
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* SA P800
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* SA E400
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* SA P400i
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* SA E200
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* SA E200i
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* SA E500
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* SA P700m
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* SA P212
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* SA P410
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* SA P410i
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* SA P411
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* SA P812
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* SA P712m
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* SA P711m
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Detecting drive failures:
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-------------------------
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To get the status of logical volumes and to detect physical drive
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failures, you can use the cciss_vol_status program found here:
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http://cciss.sourceforge.net/#cciss_utils
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Device Naming:
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--------------
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If nodes are not already created in the /dev/cciss directory, run as root:
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# cd /dev
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# ./MAKEDEV cciss
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You need some entries in /dev for the cciss device. The MAKEDEV script
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can make device nodes for you automatically. Currently the device setup
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is as follows:
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Major numbers:
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104 cciss0
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105 cciss1
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106 cciss2
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105 cciss3
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108 cciss4
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109 cciss5
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110 cciss6
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111 cciss7
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Minor numbers:
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b7 b6 b5 b4 b3 b2 b1 b0
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|----+----| |----+----|
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| +-------- Partition ID (0=wholedev, 1-15 partition)
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+-------------------- Logical Volume number
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The device naming scheme is:
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/dev/cciss/c0d0 Controller 0, disk 0, whole device
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/dev/cciss/c0d0p1 Controller 0, disk 0, partition 1
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/dev/cciss/c0d0p2 Controller 0, disk 0, partition 2
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/dev/cciss/c0d0p3 Controller 0, disk 0, partition 3
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/dev/cciss/c1d1 Controller 1, disk 1, whole device
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/dev/cciss/c1d1p1 Controller 1, disk 1, partition 1
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/dev/cciss/c1d1p2 Controller 1, disk 1, partition 2
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/dev/cciss/c1d1p3 Controller 1, disk 1, partition 3
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CCISS simple mode support
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-------------------------
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The "cciss_simple_mode=1" boot parameter may be used to prevent the driver
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from putting the controller into "performant" mode. The difference is that
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with simple mode, each command completion requires an interrupt, while with
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"performant mode" (the default, and ordinarily better performing) it is
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possible to have multiple command completions indicated by a single
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interrupt.
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SCSI tape drive and medium changer support
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------------------------------------------
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SCSI sequential access devices and medium changer devices are supported and
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appropriate device nodes are automatically created. (e.g.
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/dev/st0, /dev/st1, etc. See the "st" man page for more details.)
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You must enable "SCSI tape drive support for Smart Array 5xxx" and
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"SCSI support" in your kernel configuration to be able to use SCSI
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tape drives with your Smart Array 5xxx controller.
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Additionally, note that the driver will engage the SCSI core at init
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time if any tape drives or medium changers are detected. The driver may
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also be directed to dynamically engage the SCSI core via the /proc filesystem
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entry which the "block" side of the driver creates as
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/proc/driver/cciss/cciss* at runtime. This is best done via a script.
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For example:
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for x in /proc/driver/cciss/cciss[0-9]*
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do
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echo "engage scsi" > $x
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done
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Once the SCSI core is engaged by the driver, it cannot be disengaged
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(except by unloading the driver, if it happens to be linked as a module.)
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Note also that if no sequential access devices or medium changers are
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detected, the SCSI core will not be engaged by the action of the above
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script.
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Hot plug support for SCSI tape drives
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-------------------------------------
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Hot plugging of SCSI tape drives is supported, with some caveats.
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The cciss driver must be informed that changes to the SCSI bus
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have been made. This may be done via the /proc filesystem.
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For example:
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echo "rescan" > /proc/scsi/cciss0/1
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This causes the driver to query the adapter about changes to the
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physical SCSI buses and/or fibre channel arbitrated loop and the
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driver to make note of any new or removed sequential access devices
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or medium changers. The driver will output messages indicating what
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devices have been added or removed and the controller, bus, target and
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lun used to address the device. It then notifies the SCSI mid layer
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of these changes.
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Note that the naming convention of the /proc filesystem entries
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contains a number in addition to the driver name. (E.g. "cciss0"
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instead of just "cciss" which you might expect.)
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Note: ONLY sequential access devices and medium changers are presented
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as SCSI devices to the SCSI mid layer by the cciss driver. Specifically,
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physical SCSI disk drives are NOT presented to the SCSI mid layer. The
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physical SCSI disk drives are controlled directly by the array controller
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hardware and it is important to prevent the kernel from attempting to directly
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access these devices too, as if the array controller were merely a SCSI
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controller in the same way that we are allowing it to access SCSI tape drives.
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SCSI error handling for tape drives and medium changers
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-------------------------------------------------------
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The linux SCSI mid layer provides an error handling protocol which
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kicks into gear whenever a SCSI command fails to complete within a
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certain amount of time (which can vary depending on the command).
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The cciss driver participates in this protocol to some extent. The
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normal protocol is a four step process. First the device is told
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to abort the command. If that doesn't work, the device is reset.
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If that doesn't work, the SCSI bus is reset. If that doesn't work
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the host bus adapter is reset. Because the cciss driver is a block
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driver as well as a SCSI driver and only the tape drives and medium
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changers are presented to the SCSI mid layer, and unlike more
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straightforward SCSI drivers, disk i/o continues through the block
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side during the SCSI error recovery process, the cciss driver only
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implements the first two of these actions, aborting the command, and
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resetting the device. Additionally, most tape drives will not oblige
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in aborting commands, and sometimes it appears they will not even
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obey a reset command, though in most circumstances they will. In
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the case that the command cannot be aborted and the device cannot be
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reset, the device will be set offline.
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In the event the error handling code is triggered and a tape drive is
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successfully reset or the tardy command is successfully aborted, the
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tape drive may still not allow i/o to continue until some command
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is issued which positions the tape to a known position. Typically you
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must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example)
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before i/o can proceed again to a tape drive which was reset.
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There is a cciss_tape_cmds module parameter which can be used to make cciss
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allocate more commands for use by tape drives. Ordinarily only a few commands
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(6) are allocated for tape drives because tape drives are slow and
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infrequently used and the primary purpose of Smart Array controllers is to
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act as a RAID controller for disk drives, so the vast majority of commands
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are allocated for disk devices. However, if you have more than a few tape
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drives attached to a smart array, the default number of commands may not be
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enought (for example, if you have 8 tape drives, you could only rewind 6
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at one time with the default number of commands.) The cciss_tape_cmds module
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parameter allows more commands (up to 16 more) to be allocated for use by
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tape drives. For example:
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insmod cciss.ko cciss_tape_cmds=16
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Or, as a kernel boot parameter passed in via grub: cciss.cciss_tape_cmds=8
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