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diff --git a/Documentation/laptops/disk-shock-protection.txt b/Documentation/laptops/disk-shock-protection.txt deleted file mode 100644 index 0e6ba2663834..000000000000 --- a/Documentation/laptops/disk-shock-protection.txt +++ /dev/null @@ -1,149 +0,0 @@ -Hard disk shock protection -========================== - -Author: Elias Oltmanns <eo@nebensachen.de> -Last modified: 2008-10-03 - - -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). - - -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 this 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. - -A word of caution: The fact that the interface operates on a basis of -milliseconds may raise expectations that cannot be satisfied in -reality. In fact, the ATA specs clearly state that the time for an -unload operation to complete is vendor specific. The hint in ATA-7 -that this will typically be within 500 milliseconds apparently has -been dropped in ATA-8. - -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 device 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. 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 its libata counterpart (i.e. your disk is called /dev/hda -instead of /dev/sda), then parking the heads of one drive (drive X) -will generally not affect the mode of operation of another drive -(drive Y) on the same port as described above. It is only when a port -reset is required to recover from an exception on drive Y that further -I/O operations on that drive (and the reset itself) will be delayed -until drive X 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 systems. 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. - - -4. CREDITS ----------- - -This implementation of disk head parking has been inspired by a patch -originally published by Jon Escombe <lists@dresco.co.uk>. 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. |