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diff --git a/share/FAQ/Text/ESDI.FAQ b/share/FAQ/Text/ESDI.FAQ deleted file mode 100644 index 8d869240d6f3..000000000000 --- a/share/FAQ/Text/ESDI.FAQ +++ /dev/null @@ -1,187 +0,0 @@ - FreeBSD - Using "Mature Technology" (MFM, ESDI) hard drives - -First, please read and make sure that you understand the "diskspace" FAQ. - -The term "partition" has become overloaded when referring to an area of a -hard disk drive. I will use "slice" in this document to refer to an area -which is a "partition" to DOS FDISK. This usage is consistent with most of -current FreeBSD. I will use the word "partition" to refer to an area de- -fined by a FreeBSD disklabel, of which there is one per FreeBSD slice. The -FreeBSD partitions may contain filesystems, swap space, or be available as -raw disk devices to applications. - -This document covers the steps you will need to perform before starting the -FreeBSD installation and which are specific to these types of disk drives. - -1 Disk layout planning -2 Disk installation (may already be done) -3 Low-level formatting (may or may not be required) - -If your drive is installed and formatted properly, careful planning is all -that you need to do. - -During the installation, there is only one special step that is required. -This is also one place where the FreeBSD taxonomic convention breaks down --- the assignment of slices is called "Partitioning" in the FreeBSD proce- -dures at the time of this writing. During that step, when you assign the -FDISK slices, be sure to specify that the bad144 lists should be created -(the "B" command). - -1 Disk layout planning ----------------------- - -To be able to make the right decisions regarding the setup of slices for -FreeBSD, you need to understand that the initial boot stages for FreeBSD -rely on the ROM BIOS, but that the ROM BIOS is not used in any way once the -FreeBSD kernel is loaded. After the kernel is loaded, it uses its own -driver instead of the BIOS to access the disk. - -These older disks do not do automatic bad block management. Some con- -trollers seem to do so, but this is a feature of the ROM BIOS on that con- -troller, and therefore is not available once FreeBSD is running. Other -controllers use a different method of bad sector handling (slipping), but -this feature can also induce translations in the sectoring which will pre- -vent successful installation. Do not use automatic sector mapping or sec- -tor slipping, even if it is supported on the controller, for the same rea- -sons that you cannot use a translated disk geometry. - -To be able to use these drives, the driver has to be able to substitute -good sectors for the bad ones. The FreeBSD filesystems assume "perfect" -disks, so the bad sector handling is done in the driver. The way this is -done is that a few copies of the list of bad sectors is kept at the end of -the slice. When a slice is opened, this list is read and kept in the driv- -er. On every access to the drive, the list is consulted to see if a sub- -stitute sector, also from the end of the slice, must be used rather than -the sector that the filesystem or application is actually asking for. This -list is called the bad144 list, which name comes from a Digital Equipment -Corporation standard for keeping this information. - -There are three reasons that you would be required to use more than one -FreeBSD slice on your disk, and all of them are more probable the larger -your drive is. - -1) The FreeBSD portion of your drive will extend beyond cylinder 1023. -2) The FreeBSD portion of your drive has (or is likely to have) more than - 126 bad sectors. -3) You need more than 7 filesystems for FreeBSD. - -It is not sufficient to make sure that the entire boot filesystem is inside -of cylinder 1024, unless it just so happens that that filesystem occupies a -flawless part of the disk. To be able to read the bad144 list during the -boot process (via the ROM BIOS), the end of the slice must be within the -first 1024 cylinders. There are also some boot managers, e.g. the OS/2 -boot manager, that require a bootable slice to be entirely below cylinder -1024. - -The bad144 data format only allows for 126 sectors to be mapped. If your -drive is large, it could easily have more than this many over its entire -size. I have a 320 Mb drive which is unusually error-filled, but still -within acceptable tolerances, and it has this problem (but it also has more -than 1024 cylinders, so I'd have had to split it, anyway). - -The FreeBSD disk label has room for 8 partitions. It is not recommended -that filesystems be placed on partitions b or c, even on non-booted slices, -so that leaves 6 partitions within each slice which may contain filesys- -tems. Older versions of FreeBSD did not support filesystems on partition d -either, but the slice-handling capability has eliminated that restriction. -It may be best to avoid using partition d if you can for compatibility pur- -poses. The installation procedures skip from a to e for this reason. - -2 Disk installation -------------------- - -Physical installation is outside the scope of this document. Consult the -documentation provided by your computer, controller, and disk drive ven- -dor(s). - -3 Low-level formatting ----------------------- - -If you are starting from scratch, you may need to low-level format your -drive(s). If you have been using your drive with the intended controller -for DOS or some other system, and will not be changing the physical orien- -tation of the drive, then you can skip this step. If the drive is new, if -you are changing the physical orientation of the drive, or it has been used -with a different controller, you may need to do the low-level format. Be -aware that some drives have jumpers on them to help compensate for changes -in physical orientation (horizontal, right side, or left side), but it is -highly recommended that, if you are changing the physical orientation of -the drive, you redo the low-level format. The "sag" of the disk head arma- -ture and other effects of gravity are quite significant at the sizes of the -bits and tracks on these drives. The greater the capacity of your drive, -the more critical this becomes. With 10-40Mb MFM drives, you may get away -with it. Beyond that, you are definitely rolling dice. - -The MFM drive format is standard, and a drive formatted on one manufacturer -and model of controller should work just fine on another, but ESDI drive -formats vary between manufacturers and sometimes even between models. A -new ESDI drive (yes, they can still be found new in the box, years old), or -one that has been in use on a different controller or in a different physi- -cal orientation will definitely require reformatting. - -As the ESDI specification developed, the ability to put the error map in- -formation (Manufacturer's Defect List, or MDL) on the drive was added. -Since it was not known how the drive would be formatted, or even what the -size of the data part of the sectors would be, each bad spot is expressed -as bytes from the index and length of the bad area in bits. This informa- -tion is recorded in a few different cylinders on each track and contains -only information pertinent to the corresponding head. The most universal -place for this information is in the last cylinder. Later ESDI drives sup- -port a "phantom" cylinder at 0xfff (4095) where this information is kept -- -the actual location of this cylinder is beyond the "last" cylinder reported -for data use. If your drive does not support cylinder 0xfff, or if your -controller doesn't know how to use it, and if you wish to preserve the man- -ufacturer's defect list, do not format the last cylinder of your drive. -The format of the MDL is such that regular data operations will not work on -a track containing that information. - -As a further caveat, it as been observed that some controllers hang if the -MDL area is accessed for data use, while others simply report an error and -go on with life. You will want to be careful to not include the MDL area -in any FreeBSD slice, but you will want to be especially careful in case -your controller is one of those that hangs if you miss. - -Now that you have decided how much of the drive to format, you can proceed -with the actual format process. How this is done varies widely from con- -troller to controller. For most of them, you need to jump into a special -location in the controller ROM using the DOS DEBUG program. For a few, -special software is provided on diskette for the controller. Because these -procedures and the ways to initiate them vary so much, it is outside of the -scope of this document to describe them. Consult the manufacturer's docu- -mentation for this procedure. - -Many of the controllers have the ability to read and use the MDL. Even -though you cannot use the controller's bad block mapping capability, which -is supported through the BIOS, it may be beneficial to allow the controller -to use this information during the format process. When the drive was -tested at the factory, it was tested at the operating margins, not just op- -timal conditions. Therefore, there may be entries in the MDL that would be -missed by a run-of-the-mill data scan. If the controller is permitted to -use the MDL during formatting, many of them will format the sector with a -special flag set in the sector preamble to guarantee that that sector will -show up as bad on a read. This is, in fact, the mechanism that some con- -trollers use to handle bad sector mapping, though FreeBSD does not use the -same mechanism. We can take advantage of this feature as a 'round about -way to get the MDL represented in the bad144 list. Having the sectors -which contain a bad spot formatted as bad will make certain that you don't -use a sector where some data patterns may fail even though the initial scan -passed that sector as OK. Even if the sector doesn't produce hard errors, -it may cause soft (correctable) errors and time-consuming retries. - -Finally, FreeBSD ----------------- - -Having made your careful plans and preparations, you are ready to use -FreeBSD on your MFM or ESDI disk drive. Don't forget to request bad block -scanning during the "Partition" slice assignment, and you should be on your -way to satisfying computing. Be prepared to allow time for the bad block -scan to take place. Depending on a variety of system parameters, such as -CPU speed, controller type, disk rotational and seek speeds, and so forth, -this process will take anywhere from several minutes to hours. If you for- -get to do the scan, it is likely that the installation will fail trying to -make the filesystems, and if it should make the filesystems, it will surely -fail when you start using them. - - John Lind, Starfire Consulting Services -E-mail: john@starfire.MN.ORG USnail: PO Box 17247, Mpls MN 55417 |