On Fri, 29 Aug 2008 23:28:41 +0200 Elias Oltmanns wrote: > 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). References > + > + > +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 devices. However, > +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 I prefer: non-zero > +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 vendors > +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. --- ~Randy Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA http://linuxplumbersconf.org/ -- 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