1 <!-- $Id: esdi.sgml,v 1.6 1996/01/31 19:02:56 mpp Exp $ -->
2 <!-- The FreeBSD Documentation Project -->
5 <title>An introduction to ESDI hard disks and their use with FreeBSD</title>
6 <author>(c) 1995, Wilko Bulte, <tt/wilko@yedi.iaf.nl/
7 <date>Tue Sep 12 20:48:44 MET DST 1995</date>
9 Copyright 1995, Wilko C. Bulte, Arnhem, The Netherlands
12 This document describes the use of ESDI disks in combination
13 with the FreeBSD operating system. Contrary to popular
14 belief, this is possible and people are using ESDI based
15 systems successfully! This document tries to explain you
18 If you find something missing, plain wrong or have useful
19 comments on how to improve
20 the document please send mail to <tt/wilko@yedi.iaf.nl/
24 <sect1><heading>Using ESDI hard disks<label id="esdi"></heading>
26 <p><em>Copyright © 1995, &a.wilko;.<newline>24 September 1995.</em>
28 ESDI is an acronym that means Enhanced Small Device Interface.
29 It is loosely based on the good old ST506/412 interface originally
30 devised by Seagate Technology, the makers of the first affordable
31 5.25" winchester disk.
33 The acronym says Enhanced, and rightly so. In the first place
34 the speed of the interface is higher, 10 or 15 Mbits/second
35 instead of the 5 Mbits/second of ST412 interfaced drives.
36 Secondly some higher level commands are added, making the ESDI
37 interface somewhat 'smarter' to the operating system driver
38 writers. It is by no means as smart as SCSI by the way. ESDI
39 is standardized by ANSI.
41 Capacities of the drives are boosted by putting more sectors
42 on each track. Typical is 35 sectors per track, high capacity
43 drives I have seen were up to 54 sectors/track.
45 Although ESDI has been largely obsoleted by IDE and SCSI interfaces,
46 the availability of free or cheap surplus drives makes them
47 ideal for low (or now) budget systems.
49 <sect2><heading>Concepts of ESDI</heading>
51 <sect3><heading>Physical connections</heading>
53 The ESDI interface uses two cables connected to each drive.
54 One cable is a 34 pin flat cable edge connector that carries
55 the command and status signals from the controller to the
56 drive and vice-versa. The command cable is daisy chained
57 between all the drives. So, it forms a bus onto which all
60 The second cable is a a 20 pin flat cable edge connector that
61 carries the data to and from the drive. This cable is radially
62 connected, so each drive has its own direct connection to the
65 To the best of my knowledge PC ESDI controllers are limited
66 to using a maximum of 2 drives per controller. This is
67 compatibility feature(?) left over from the WD1003 standard
68 that reserves only a single bit for device addressing.
70 <sect3><heading>Device addressing</heading>
72 On each command cable a maximum of 7 devices and 1 controller
73 can be present. To enable the controller to uniquely
74 identify which drive it addresses, each ESDI device is equipped
75 with jumpers or switches to select the devices address.
77 On PC type controllers the first drive is set to address 0,
78 the second disk to address 1. <it>Always make sure</it> you
79 set each disk to an unique address! So, on a PC with its
80 two drives/controller maximum the first drive is drive 0, the
83 <sect3><heading>Termination</heading>
85 The daisy chained command cable (the 34 pin cable remember?)
86 needs to be terminated at the last drive on the chain.
87 For this purpose ESDI drives come with a termination resistor
88 network that can be removed or disabled by a jumper when it
91 So, one and <it>only</it> one drive, the one at
92 the farthest end of the command
93 cable has its terminator installed/enabled. The controller
94 automatically terminates the other end of the cable.
95 Please note that this implies that the controller must be
96 at one end of the cable and <it>not</it> in the middle.
98 <sect2><heading>Using ESDI disks with FreeBSD</heading>
100 Why is ESDI such a pain to get working in the first place?
102 People who tried ESDI disks with FreeBSD are known to have
103 developed a profound sense of frustration. A combination of
104 factors works against you to produce effects that are
105 hard to understand when you have never seen them before.
107 This has also led to the popular legend ESDI and FreeBSD
109 The following sections try to list all the pitfalls and
112 <sect3><heading>ESDI speed variants</heading>
114 As briefly mentioned before, ESDI comes in two speed flavors.
115 The older drives and controllers use a 10 Mbits/second
116 data transfer rate. Newer stuff uses 15 Mbits/second.
118 It is not hard to imagine that 15 Mbits/second drive cause
119 problems on controllers laid out for 10 Mbits/second.
120 As always, consult your controller <it>and</it> drive
121 documentation to see if things match.
123 <sect3><heading>Stay on track</heading>
125 Mainstream ESDI drives use 34 to 36 sectors per track.
126 Most (older) controllers cannot handle more than this
128 Newer, higher capacity, drives use higher numbers of sectors
129 per track. For instance, I own a 670 Mb drive that has
130 54 sectors per track.
132 In my case, the controller could not handle this number
133 of sectors. It proved to work well except that it only
134 used 35 sectors on each track. This meant losing a
137 Once again, check the documentation of your hardware for
138 more info. Going out-of-spec like in the example might
139 or might not work. Give it a try or get another more
142 <sect3><heading>Hard or soft sectoring</heading>
144 Most ESDI drives allow hard or soft sectoring to be
145 selected using a jumper. Hard sectoring means that the
146 drive will produce a sector pulse on the start of each
147 new sector. The controller uses this pulse to tell when
148 it should start to write or read.
150 Hard sectoring allows a selection of sector size (normally
151 256, 512 or 1024 bytes per formatted sector). FreeBSD uses
152 512 byte sectors. The number of sectors per track also varies
153 while still using the same number of bytes per formatted sector.
154 The number of <em>unformatted</em> bytes per sector varies,
155 dependent on your controller it needs more or less overhead
156 bytes to work correctly. Pushing more sectors on a track
157 of course gives you more usable space, but might give
158 problems if your controller needs more bytes than the
161 In case of soft sectoring, the controller itself determines
162 where to start/stop reading or writing. For ESDI
163 hard sectoring is the default (at least on everything
164 I came across). I never felt the urge to try soft sectoring.
166 In general, experiment with sector settings before you install
167 FreeBSD because you need to re-run the low-level format
170 <sect3><heading>Low level formatting</heading>
172 ESDI drives need to be low level formatted before they
173 are usable. A reformat is needed whenever you figgle
174 with the number of sectors/track jumpers or the
175 physical orientation of the drive (horizontal, vertical).
176 So, first think, then format.
177 The format time must not be underestimated, for big
178 disks it can take hours.
180 After a low level format, a surface scan is done to
181 find and flag bad sectors. Most disks have a
182 manufacturer bad block list listed on a piece of paper
183 or adhesive sticker. In addition, on most disks the
184 list is also written onto the disk.
185 Please use the manufacturer's list. It is much easier
186 to remap a defect now than after FreeBSD is installed.
188 Stay away from low-level formatters that mark all
189 sectors of a track as bad as soon as they find one
190 bad sector. Not only does this waste space, it also
191 and more importantly causes you grief with bad144
192 (see the section on bad144).
194 <sect3><heading>Translations</heading>
196 Translations, although not exclusively a ESDI-only problem,
197 might give you real trouble.
198 Translations come in multiple flavors. Most of them
199 have in common that they attempt to work around the
200 limitations posed upon disk geometries by the original
201 IBM PC/AT design (thanks IBM!).
203 First of all there is the (in)famous 1024 cylinder limit.
204 For a system to be able to boot, the stuff (whatever
205 operating system) must be in the first 1024 cylinders
206 of a disk. Only 10 bits are available to encode the
207 cylinder number. For the number of sectors the limit
209 When you combine the 1024 cylinder limit with the 16 head
210 limit (also a design feature) you max out at fairly limited
213 To work around this problem, the manufacturers of ESDI
214 PC controllers added a BIOS prom extension on their boards.
215 This BIOS extension handles disk I/O for booting (and for
216 some operating systems <it>all</it> disk I/O) by using
217 translation. For instance, a big drive might be presented
218 to the system as having 32 heads and 64 sectors/track.
219 The result is that the number of cylinders is reduced to
220 something below 1024 and is therefore usable by the system
222 It is noteworthy to know that FreeBSD does not use the
223 BIOS after its kernel has started. More on this later.
225 A second reason for translations is the fact that most
226 older system BIOSes could only handle drives with 17 sectors
227 per track (the old ST412 standard). Newer system BIOSes
228 usually have a user-defined drive type (in most cases this is
231 <em>Whatever you do to translations after reading this document,
232 keep in mind that if you have multiple operating systems on the
233 same disk, all must use the same translation</em>
235 While on the subject of translations, I have seen one controller
236 type (but there are probably more like this) offer the option
237 to logically split a drive in multiple partitions as a BIOS
238 option. I had select 1 drive == 1 partition because this
239 controller wrote this info onto the disk. On power-up it
240 read the info and presented itself to the system based on
241 the info from the disk.
243 <sect3><heading>Spare sectoring</heading>
245 Most ESDI controllers offer the possibility to remap bad sectors.
246 During/after the low-level format of the disk bad sectors are
247 marked as such, and a replacement sector is put in place
248 (logically of course) of the bad one.
250 In most cases the remapping is done by using N-1 sectors on
251 each track for actual data storage, and sector N itself is
252 the spare sector. N is the total number of sectors physically
253 available on the track.
254 The idea behind this is that the operating system sees
255 a 'perfect' disk without bad sectors. In the case of
256 FreeBSD this concept is not usable.
258 The problem is that the translation from <it>bad</it> to <it>good</it>
259 is performed by the BIOS of the ESDI controller. FreeBSD,
260 being a true 32 bit operating system, does not use the BIOS
261 after it has been booted. Instead, it has device drivers that
262 talk directly to the hardware.
264 <em>So: don't use spare sectoring, bad block remapping or
265 whatever it may be called by the controller manufacturer when you
266 want to use the disk for FreeBSD.</em>
268 <sect3><heading>Bad block handling</heading>
270 The preceding section leaves us with a problem. The controller's
271 bad block handling is not usable and still FreeBSD's filesystems
272 assume perfect media without any flaws.
273 To solve this problem, FreeBSD use the <it>bad144</it> tool.
274 Bad144 (named after a Digital Equipment standard for bad block
275 handling) scans a FreeBSD slice for bad blocks. Having found
276 these bad blocks, it writes a table with the offending block
277 numbers to the end of the FreeBSD slice.
279 When the disk is in operation, the disk accesses are checked
280 against the table read from the disk. Whenever a block number
281 is requested that is in the bad144 list, a replacement block
282 (also from the end of the FreeBSD slice) is used.
283 In this way, the bad144 replacement scheme presents 'perfect'
284 media to the FreeBSD filesystems.
286 There are a number of potential pitfalls associated with
288 First of all, the slice cannot have more than 126 bad sectors.
289 If your drive has a high number of bad sectors, you might need
290 to divide it into multiple FreeBSD slices each containing less
291 than 126 bad sectors. Stay away from low-level format programs
292 that mark <em>every</em> sector of a track as bad when
293 they find a flaw on the track. As you can imagine, the
294 126 limit is quickly reached when the low-level format is done
297 Second, if the slice contains the root filesystem, the slice
298 should be within the 1024 cylinder BIOS limit. During the
299 boot process the bad144 list is read using the BIOS and this
300 only succeeds when the list is within the 1024 cylinder limit.
301 <em>Note</em> that the restriction is not that only the root
302 <em>filesystem</em> must be within the 1024 cylinder limit, but
303 rather the entire <em>slice</em> that contains the root filesystem.
306 <sect3><heading>Kernel configuration</heading>
308 ESDI disks are handled by the same <it>wd</it>driver as
309 IDE and ST412 MFM disks. The <it>wd</it> driver should work
310 for all WD1003 compatible interfaces.
312 Most hardware is jumperable for one of two different I/O
313 address ranges and IRQ lines. This allows you to have
314 two wd type controllers in one system.
316 When your hardware allows non-standard strappings, you
317 can use these with FreeBSD as long as you enter the
318 correct info into the kernel config file.
319 An example from the kernel config file (they live in
320 <tt>/sys/i386/conf</tt> BTW).
323 # First WD compatible controller
324 controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr
325 disk wd0 at wdc0 drive 0
326 disk wd1 at wdc0 drive 1
328 # Second WD compatible controller
329 controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr
330 disk wd2 at wdc1 drive 0
331 disk wd3 at wdc1 drive 1
335 <sect3><heading>Tuning your ESDI kernel setup</heading>
339 <sect2><heading>Particulars on ESDI hardware</heading>
341 <sect3><heading>Adaptec 2320 controllers</heading>
343 I successfully installed FreeBSD onto a ESDI disk controlled by a
344 ACB-2320. No other operating system was present on the disk.
346 To do so I low level formatted the disk using NEFMT.EXE
347 (<it>ftp</it>able from <it>www.adaptec.com</it>) and answered NO
348 to the question whether the disk should be formatted with a
349 spare sector on each track. The BIOS on the ACD-2320 was
350 disabled. I used the 'free configurable' option in the system
351 BIOS to allow the BIOS to boot it.
353 Before using NEFMT.EXE I tried to format the disk using the
354 ACB-2320 BIOS builtin formatter. This proved to be a show stopper,
355 because it did not give me an option to disable spare sectoring.
356 With spare sectoring enabled the FreeBSD installation
357 process broke down on the bad144 run.
359 Please check carefully which ACB-232xy variant you have. The
360 x is either 0 or 2, indicating a controller without or with
361 a floppy controller on board.
363 The y is more interesting. It can either be a blank,
364 a "A-8" or a "D". A blank indicates a plain 10 Mbits/second
365 controller. An "A-8" indicates a 15 Mbits/second controller
366 capable of handling 52 sectors/track.
367 A "D" means a 15 Mbits/second controller that can also
368 handle drives with > 36 sectors/track (also 52 ?).
370 All variations should be capable of using 1:1 interleaving. Use 1:1,
371 FreeBSD is fast enough to handle it.
373 <sect3><heading>Western Digital WD1007 controllers</heading>
375 I successfully installed FreeBSD onto a ESDI disk controlled by a
376 WD1007 controller. To be precise, it was a WD1007-WA2. Other
377 variations of the WD1007 do exist.
379 To get it to work, I had to disable the sector translation and
380 the WD1007's onboard BIOS. This implied I could not use
381 the low-level formatter built into this BIOS. Instead, I grabbed
382 WDFMT.EXE from www.wdc.com Running this formatted my drive
385 <sect3><heading>Ultrastor U14F controllers</heading>
387 According to multiple reports from the net, Ultrastor ESDI
388 boards work OK with FreeBSD. I lack any further info on
393 <sect2><heading>Tracking down problems</heading>
397 <sect2><heading>Further reading<label id="esdi:further-reading"></>
399 If you intend to do some serious ESDI hacking, you might want to
400 have the official standard at hand:
402 The latest ANSI X3T10 committee document is:
404 <item>Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991]
405 [X3T10/792D Rev 11]
407 On Usenet the newsgroup <htmlurl url="news:comp.periphs"
408 name="comp.periphs"> is a noteworthy place to look
411 The World Wide Web (WWW) also proves to be a very handy info source:
412 For info on Adaptec ESDI controllers see <htmlurl
413 url="http://www.adaptec.com/">.
414 For info on Western Digital controllers see <htmlurl
415 url="http://www.wdc.com/">.
419 Andrew Gordon for sending me an Adaptec 2320 controller and ESDI disk
projects / FreeBSD / FreeBSD.git / blob