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Message-ID: <20080829211345.4355.5630.stgit@denkblock.local> Date: Fri, 29 Aug 2008 23:28:41 +0200 From: Elias Oltmanns <eo@...ensachen.de> To: Alan Cox <alan@...rguk.ukuu.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Bartlomiej Zolnierkiewicz <bzolnier@...il.com>, Jeff Garzik <jeff@...zik.org>, Randy Dunlap <randy.dunlap@...cle.com>, Tejun Heo <htejun@...il.com> Cc: linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH 4/4] Add documentation for hard disk shock protection interface Put some information (and pointers to more) into the kernel's doc tree, describing briefly the interface to the kernel's disk head unloading facility. Information about how to set up a complete shock protection system under GNU/Linux can be found on the web and is referenced accordingly. Signed-off-by: Elias Oltmanns <eo@...ensachen.de> --- Documentation/laptops/disk-shock-protection.txt | 131 +++++++++++++++++++++++ 1 files changed, 131 insertions(+), 0 deletions(-) create mode 100644 Documentation/laptops/disk-shock-protection.txt diff --git a/Documentation/laptops/disk-shock-protection.txt b/Documentation/laptops/disk-shock-protection.txt new file mode 100644 index 0000000..bd483a3 --- /dev/null +++ b/Documentation/laptops/disk-shock-protection.txt @@ -0,0 +1,131 @@ +Hard disk shock protection +========================== + +Author: Elias Oltmanns <eo@...ensachen.de> +Last modified: 2008-08-28 + + +0. Contents +----------- + +1. Intro +2. The interface +3. References +4. CREDITS + + +1. Intro +-------- + +ATA/ATAPI-7 specifies the IDLE IMMEDIATE command with unload feature. +Issuing this command should cause the drive to switch to idle mode and +unload disk heads. This feature is being used in modern laptops in +conjunction with accelerometers and appropriate software to implement +a shock protection facility. The idea is to stop all I/O operations on +the internal hard drive and park its heads on the ramp when critical +situations are anticipated. The desire to have such a feature +available on GNU/Linux systems has been the original motivation to +implement a generic disk head parking interface in the Linux kernel. +Please note, however, that other components have to be set up on your +system in order to get disk shock protection working (see section +3. Referneces below for pointers to more information about that). + + +2. The interface +---------------- + +The interface works as follows: Writing an integer value to +/sys/block/*/device/unload_heads will take the heads of the respective +drive off the platter and block all I/O operations for the specified +number of seconds. When the timeout expires and no further disk head +park request has been issued in the meantime, normal operation will be +resumed. The maximal value accepted for a timeout is 30 seconds. +However, you can always reset a running timer to any value between 0 +and 30 by issuing a subsequent head park request before the timer of +the previous one has expired. In particular, the total timeout can +exceed 30 seconds and, more importantly, you can abort a timer and +resume normal operation immediately by specifying a timeout of 0. +Reading from /sys/block/*/device/unload_heads will report zero if no +timer is running and the number of seconds until the timer expires +otherwise. + +There is a technical detail of this implementation that may cause some +confusion and should be discussed here. When a head park request has +been issued to a device successfully, all I/O operations on the +controller port this device is attached to will be deferred. That is +to say, any other device that may be connected to the same port will +be affected too. For that reason, head parking requests will be sent +to all devices that support this feature sharing the same port before +that port is taken offline, as it were. As far as PATA (old style IDE) +configurations are concerned, there can only be two devices attached +to any single port. In SATA world we have port multipliers which means +that a user issued head parking request to one device may actually +result in stopping I/O to a whole bunch of deviices. Hwoever, since +this feature is supposed to be used on laptops and does not seem to be +very useful in any other environment, there will be mostly one device +per port. Even if the CD/DVD writer happens to be connected to the +same port as the hard drive, it generally *should* recover just fine +from the occasional buffer under-run incurred by a head park request +to the HD. + +Write access to /sys/block/*/device/unload_heads is denied with +-EOPNOTSUPP if the device does not support the unload feature. Read +access, on the other hand, is granted on all devices, so it is easy to +find out whether two devices share the same port and are subject to +the limitation described in the previous paragraph. Just do, for +example: + +# echo 30 > /sys/block/sda/device/unload_heads + +and check whether + +# cat /sys/block/device/sdb/unload_heads + +gives you a nonzero value (assuming, of course, there actually are +devices sda and sdb up and running in your system). + +Finally, there are some hard drives that only comply with an earlier +version of the ATA standard than ATA-7, but do support the unload +feature nonetheless. Unfortunately, there is no safe way Linux can +detect these devices, so you won't be able to write to the +unload_heads attribute. If you know that your device really does +support the unload feature (for instance, because the vendor of your +laptop or the hard drive itself told you so), the you can tell the +kernel to enable the usage of this feature for that drive by means of +the unload_feature attribute: + +# echo 1 > /sys/block/*/device/unload_feature + +will enable the feature on that particular device, and giving 0 +instead of 1 will disable it again. + + +3. References +------------- + +There are several laptops from different brands featuring shock +protection capabilities. As manufacturers have refused to support open +source development of the required software components so far, Linux +support for shock protection varies considerably between different +hardware implementations. Ideally, this section should contain a list +of pointers at different projects aiming at an implementation of shock +protection on different systeems. Unfortunately, I only know of a +single project which, although still considered experimental, is fit +for use. Please feel free to add projects that have been the victims +of my ignorance. + +- http://www.thinkwiki.org/wiki/HDAPS + See this page for information about Linux support of the hard disk + active protection system as implemented in IBM/Lenovo Thinkpads. + (FIXME: The information there will have to be updated once this + patch has been approved or the user interface has been agreed upon + at least.) + + +4. CREDITS +---------- + +This implementation of disk head parking has been based on a patch +originally published by Jon Escombe <lists@...sco.co.uk>. Assisted by +various kernel developers, the author of this document has rewritten +the original patch in order to make it fit for upstream submission. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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