1 ==========================
2 Hard disk shock protection
3 ==========================
4
5 Author: Elias Oltmanns <eo@nebensachen.de>
6
7 Last modified: 2008-10-03
8
9
10 .. 0. Contents
11
12 1. Intro
13 2. The interface
14 3. References
15 4. CREDITS
16
17
18 1. Intro
19 --------
20
21 ATA/ATAPI-7 specifies the IDLE IMMEDIATE comma
22 Issuing this command should cause the drive to
23 unload disk heads. This feature is being used
24 conjunction with accelerometers and appropriat
25 a shock protection facility. The idea is to st
26 the internal hard drive and park its heads on
27 situations are anticipated. The desire to have
28 available on GNU/Linux systems has been the or
29 implement a generic disk head parking interfac
30 Please note, however, that other components ha
31 system in order to get disk shock protection w
32 section 3. References below for pointers to mo
33 that).
34
35
36 2. The interface
37 ----------------
38
39 For each ATA device, the kernel exports the fi
40 `block/*/device/unload_heads` in sysfs (here a
41 /sys). Access to `/sys/block/*/device/unload_h
42 -EOPNOTSUPP if the device does not support the
43 Otherwise, writing an integer value to this fi
44 of the respective drive off the platter and bl
45 for the specified number of milliseconds. When
46 no further disk head park request has been iss
47 normal operation will be resumed. The maximal
48 timeout is 30000 milliseconds. Exceeding this
49 -EOVERFLOW, but heads will be parked anyway an
50 set to 30 seconds. However, you can always cha
51 value between 0 and 30000 by issuing a subsequ
52 before the timeout of the previous one has exp
53 total timeout can exceed 30 seconds and, more
54 cancel a previously set timeout and resume nor
55 immediately by specifying a timeout of 0. Valu
56 with -EINVAL (see below for the special meanin
57 timeout specified for a recent head park reque
58 reading from `/sys/block/*/device/unload_heads
59 of milliseconds remaining until normal operati
60 otherwise, reading the unload_heads attribute
61
62 For example, do the following in order to park
63 /dev/sda and stop all I/O operations for five
64
65 # echo 5000 > /sys/block/sda/device/un
66
67 A simple::
68
69 # cat /sys/block/sda/device/unload_hea
70
71 will show you how many milliseconds are left b
72 will be resumed.
73
74 A word of caution: The fact that the interface
75 milliseconds may raise expectations that canno
76 reality. In fact, the ATA specs clearly state
77 unload operation to complete is vendor specifi
78 that this will typically be within 500 millise
79 been dropped in ATA-8.
80
81 There is a technical detail of this implementa
82 confusion and should be discussed here. When a
83 been issued to a device successfully, all I/O
84 controller port this device is attached to wil
85 to say, any other device that may be connected
86 be affected too. The only exception is that a
87 request to that other device will be executed
88 operations on that port will be deferred until
89 for either device on the port has expired. As
90 IDE) configurations are concerned, there can o
91 attached to any single port. In SATA world we
92 which means that a user-issued head parking re
93 actually result in stopping I/O to a whole bun
94 since this feature is supposed to be used on l
95 to be very useful in any other environment, th
96 device per port. Even if the CD/DVD writer hap
97 the same port as the hard drive, it generally
98 fine from the occasional buffer under-run incu
99 request to the HD. Actually, when you are usin
100 than its libata counterpart (i.e. your disk is
101 instead of /dev/sda), then parking the heads o
102 will generally not affect the mode of operatio
103 (drive Y) on the same port as described above.
104 reset is required to recover from an exception
105 I/O operations on that drive (and the reset it
106 until drive X is no longer in the parked state
107
108 Finally, there are some hard drives that only
109 version of the ATA standard than ATA-7, but do
110 feature nonetheless. Unfortunately, there is n
111 detect these devices, so you won't be able to
112 unload_heads attribute. If you know that your
113 support the unload feature (for instance, beca
114 laptop or the hard drive itself told you so),
115 kernel to enable the usage of this feature for
116 the special value -1 to the unload_heads attri
117
118 # echo -1 > /sys/block/sda/device/unlo
119
120 will enable the feature for /dev/sda, and givi
121 disable it again.
122
123
124 3. References
125 -------------
126
127 There are several laptops from different vendo
128 protection capabilities. As manufacturers have
129 source development of the required software co
130 support for shock protection varies considerab
131 hardware implementations. Ideally, this sectio
132 of pointers at different projects aiming at an
133 protection on different systems. Unfortunately
134 single project which, although still considere
135 for use. Please feel free to add projects that
136 of my ignorance.
137
138 - https://www.thinkwiki.org/wiki/HDAPS
139
140 See this page for information about Linux su
141 active protection system as implemented in I
142
143
144 4. CREDITS
145 ----------
146
147 This implementation of disk head parking has b
148 originally published by Jon Escombe <lists@dres
149 to develop an implementation of this feature t
150 into mainline have been aided by various kerne
151 particular by Tejun Heo and Bartlomiej Zolnier
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