scsi-changer.rst (6505B)
1.. SPDX-License-Identifier: GPL-2.0 2 3======================================== 4README for the SCSI media changer driver 5======================================== 6 7This is a driver for SCSI Medium Changer devices, which are listed 8with "Type: Medium Changer" in /proc/scsi/scsi. 9 10This is for *real* Jukeboxes. It is *not* supported to work with 11common small CD-ROM changers, neither one-lun-per-slot SCSI changers 12nor IDE drives. 13 14Userland tools available from here: 15 http://linux.bytesex.org/misc/changer.html 16 17 18General Information 19------------------- 20 21First some words about how changers work: A changer has 2 (possibly 22more) SCSI ID's. One for the changer device which controls the robot, 23and one for the device which actually reads and writes the data. The 24later may be anything, a MOD, a CD-ROM, a tape or whatever. For the 25changer device this is a "don't care", he *only* shuffles around the 26media, nothing else. 27 28 29The SCSI changer model is complex, compared to - for example - IDE-CD 30changers. But it allows to handle nearly all possible cases. It knows 314 different types of changer elements: 32 33 =============== ================================================== 34 media transport this one shuffles around the media, i.e. the 35 transport arm. Also known as "picker". 36 storage a slot which can hold a media. 37 import/export the same as above, but is accessible from outside, 38 i.e. there the operator (you !) can use this to 39 fill in and remove media from the changer. 40 Sometimes named "mailslot". 41 data transfer this is the device which reads/writes, i.e. the 42 CD-ROM / Tape / whatever drive. 43 =============== ================================================== 44 45None of these is limited to one: A huge Jukebox could have slots for 46123 CD-ROM's, 5 CD-ROM readers (and therefore 6 SCSI ID's: the changer 47and each CD-ROM) and 2 transport arms. No problem to handle. 48 49 50How it is implemented 51--------------------- 52 53I implemented the driver as character device driver with a NetBSD-like 54ioctl interface. Just grabbed NetBSD's header file and one of the 55other linux SCSI device drivers as starting point. The interface 56should be source code compatible with NetBSD. So if there is any 57software (anybody knows ???) which supports a BSDish changer driver, 58it should work with this driver too. 59 60Over time a few more ioctls where added, volume tag support for example 61wasn't covered by the NetBSD ioctl API. 62 63 64Current State 65------------- 66 67Support for more than one transport arm is not implemented yet (and 68nobody asked for it so far...). 69 70I test and use the driver myself with a 35 slot cdrom jukebox from 71Grundig. I got some reports telling it works ok with tape autoloaders 72(Exabyte, HP and DEC). Some People use this driver with amanda. It 73works fine with small (11 slots) and a huge (4 MOs, 88 slots) 74magneto-optical Jukebox. Probably with lots of other changers too, most 75(but not all :-) people mail me only if it does *not* work... 76 77I don't have any device lists, neither black-list nor white-list. Thus 78it is quite useless to ask me whenever a specific device is supported or 79not. In theory every changer device which supports the SCSI-2 media 80changer command set should work out-of-the-box with this driver. If it 81doesn't, it is a bug. Either within the driver or within the firmware 82of the changer device. 83 84 85Using it 86-------- 87 88This is a character device with major number is 86, so use 89"mknod /dev/sch0 c 86 0" to create the special file for the driver. 90 91If the module finds the changer, it prints some messages about the 92device [ try "dmesg" if you don't see anything ] and should show up in 93/proc/devices. If not.... some changers use ID ? / LUN 0 for the 94device and ID ? / LUN 1 for the robot mechanism. But Linux does *not* 95look for LUNs other than 0 as default, because there are too many 96broken devices. So you can try: 97 98 1) echo "scsi add-single-device 0 0 ID 1" > /proc/scsi/scsi 99 (replace ID with the SCSI-ID of the device) 100 2) boot the kernel with "max_scsi_luns=1" on the command line 101 (append="max_scsi_luns=1" in lilo.conf should do the trick) 102 103 104Trouble? 105-------- 106 107If you insmod the driver with "insmod debug=1", it will be verbose and 108prints a lot of stuff to the syslog. Compiling the kernel with 109CONFIG_SCSI_CONSTANTS=y improves the quality of the error messages a lot 110because the kernel will translate the error codes into human-readable 111strings then. 112 113You can display these messages with the dmesg command (or check the 114logfiles). If you email me some question because of a problem with the 115driver, please include these messages. 116 117 118Insmod options 119-------------- 120 121debug=0/1 122 Enable debug messages (see above, default: 0). 123 124verbose=0/1 125 Be verbose (default: 1). 126 127init=0/1 128 Send INITIALIZE ELEMENT STATUS command to the changer 129 at insmod time (default: 1). 130 131timeout_init=<seconds> 132 timeout for the INITIALIZE ELEMENT STATUS command 133 (default: 3600). 134 135timeout_move=<seconds> 136 timeout for all other commands (default: 120). 137 138dt_id=<id1>,<id2>,... / dt_lun=<lun1>,<lun2>,... 139 These two allow to specify the SCSI ID and LUN for the data 140 transfer elements. You likely don't need this as the jukebox 141 should provide this information. But some devices don't ... 142 143vendor_firsts=, vendor_counts=, vendor_labels= 144 These insmod options can be used to tell the driver that there 145 are some vendor-specific element types. Grundig for example 146 does this. Some jukeboxes have a printer to label fresh burned 147 CDs, which is addressed as element 0xc000 (type 5). To tell the 148 driver about this vendor-specific element, use this:: 149 150 $ insmod ch \ 151 vendor_firsts=0xc000 \ 152 vendor_counts=1 \ 153 vendor_labels=printer 154 155 All three insmod options accept up to four comma-separated 156 values, this way you can configure the element types 5-8. 157 You likely need the SCSI specs for the device in question to 158 find the correct values as they are not covered by the SCSI-2 159 standard. 160 161 162Credits 163------- 164 165I wrote this driver using the famous mailing-patches-around-the-world 166method. With (more or less) help from: 167 168 - Daniel Moehwald <moehwald@hdg.de> 169 - Dane Jasper <dane@sonic.net> 170 - R. Scott Bailey <sbailey@dsddi.eds.com> 171 - Jonathan Corbet <corbet@lwn.net> 172 173Special thanks go to 174 175 - Martin Kuehne <martin.kuehne@bnbt.de> 176 177for a old, second-hand (but full functional) cdrom jukebox which I use 178to develop/test driver and tools now. 179 180Have fun, 181 182 Gerd 183 184Gerd Knorr <kraxel@bytesex.org>