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This is to allow number of commands reserved for use by SCSI tape drives and medium changers to be adjusted at driver load time via the kernel parameter cciss_tape_cmds, with a default value of 6, and a range of 2 - 16 inclusive. Previously, the driver limited the number of commands which could be queued to the SCSI half of the the driver to only 2. This is to fix the problem that if you had more than two tape drives, you couldn't, for example, erase or rewind them all at the same time. Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
187 lines
7.1 KiB
Plaintext
187 lines
7.1 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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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 not engage the SCSI core at init
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time. The driver must be directed to dynamically engage the SCSI core via
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the /proc filesystem entry which the "block" side of the driver creates as
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/proc/driver/cciss/cciss* at runtime. This is because at driver init time,
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the SCSI core may not yet be initialized (because the driver is a block
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driver) and attempting to register it with the SCSI core in such a case
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would cause a hang. This is best done via an initialization script
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(typically in /etc/init.d, but could vary depending on distribution).
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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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