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@xxxxxxxxxxxxxx> --- 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@xxxxxxxxxxxxxx> +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@xxxxxxxxxxxx>. 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-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
