I found one typo here...can be fixed up by hand I think. On Wed, Sep 17, 2008 at 9:40 AM, Elias Oltmanns <eo@xxxxxxxxxxxxxx> 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 | 144 +++++++++++++++++++++++ > 1 files changed, 144 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..1f93462 > --- /dev/null > +++ b/Documentation/laptops/disk-shock-protection.txt > @@ -0,0 +1,144 @@ > +Hard disk shock protection > +========================== > + > +Author: Elias Oltmanns <eo@xxxxxxxxxxxxxx> > +Last modified: 2008-09-16 > + > + > +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. References below for pointers to more information about that). Unfortunate place for a line break: "section 3" should be on one line if possible. Otherwise the "3. References" looks like section header with mangled white space (at first glance). > + > + > +2. The interface > +---------------- > + > +For each ATA device the kernel exports the file > +block/*/device/unload_heads in sysfs (here assumed to be mounted under > +/sys). Access to /sys/block/*/device/unload_heads is denied with > +-EOPNOTSUPP if the device does not support the unload feature. > +Otherwise, writing an integer value to file will take the heads of the > +respective drive off the platter and block all I/O operations for the > +specified number of milliseconds. 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 > +30000 milliseconds. Exceeding this limit will return -EOVERFLOW, but > +heads will be parked anyway and the timeout will be set to 30 seconds. > +However, you can always change a timeout to any value between 0 and > +30000 by issuing a subsequent head park request before the timeout of > +the previous one has expired. In particular, the total timeout can > +exceed 30 seconds and, more importantly, you can cancel a previously > +set timeout and resume normal operation immediately by specifying a > +timeout of 0. Values below -2 are rejected with -EINVAL (see below for > +the special meaning of -1 and -2). If the timeout specified for a > +recent head park request has not yet expired, reading from > +/sys/block/*/device/unload_heads will report the number of > +milliseconds remaining until normal operation will be resumed; > +otherwise, reading the unload_heads attribute will return 0. > + > +For example, do the following in order to park the heads of drive > +/dev/sda and stop all I/O operations for five seconds: > + > +# echo 5000 > /sys/block/sda/device/unload_heads > + > +A simple > + > +# cat /sys/block/sda/device/unload_heads > + > +will show you how many milliseconds are left before normal operation > +will be resumed. > + > +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. The only exception is that a subsequent head unload > +request to that other devvice will be executed immediately. Further > +operations on that port will be deferred until the timeout specified > +for either device on the port has expired. 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 devices. Hwoever, Typo: However > +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. Actually, when you are using an ide driver rather > +than it's libata counterpart (i.e. your disk is called /dev/hda > +instead of /dev/sda), then parking the heads of drive A will generally > +not affect the mode of operation of drive B on the same port as > +described above. It is only when a port reset is required to recover > +from an exception on drive B that further I/O operations on that drive > +(and the reset itself) will be delayed until drive A is no longer in > +the parked state. > + > +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), then you can tell the > +kernel to enable the usage of this feature for that drive by writing > +the special value -1 to the unload_heads attribute: > + > +# echo -1 > /sys/block/sda/device/unload_heads > + > +will enable the feature for /dev/sda, and giving -2 instead of -1 will > +disable it again. > + > + > +3. References > +------------- > + > +There are several laptops from different vendors 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.) Does this still belong here? > + > + > +4. CREDITS > +---------- > + > +This implementation of disk head parking has been inspired by a patch > +originally published by Jon Escombe <lists@xxxxxxxxxxxx>. My efforts > +to develop an implementation of this feature that is fit to be merged > +into mainline have been aided by various kernel developers, in > +particular by Tejun Heo and Bartlomiej Zolnierkiewicz. otherwise looks pretty good - thanks! grant > > > -- > 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 > -- 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
