Hard Drives and NetWare: A Brief Description and Usage Summary By Mickey Applebaum Wasatch Education Systems/NetWire Sysop Since the early days of operation, drastic changes have been made in the way computers and NetWare deal with the various types of drives and controllers. This article briefly outlines drive types and the restrictions that apply to each, and explains how to prepare drives for use with NetWare. (The following information is gathered from six years of working with Novell's NetWare products and various third-party programs to allow different drive types to work properly with the various versions of NetWare from v4.57a onward.) Because NetWare for the PC was first designed to operate on IBM and compatible PC XT computers, NetWare relied on the hard disk controller's BIOS to set up the drive properly. This method was a rather simplistic way of accessing the hard drives and led to problems in configuring nonstandard size drives. At this time, two options were feasibly available to the general PC marketplace: The first was Modified Frequency Modulation (MFM) encoded controllers, and the second was Run Length Limited (RLL) encoded controllers. For this discussion, the main difference between the two is that an MFM controller formats a disk at 17 sectors per track, while an RLL controller does either 21, 26, 27, or 34 sectors per track. With 286-based NetWare, Novell engineers decided there was a better way to get the drives physical configuration for number of heads, cylinders (also known as tracks), sectors per track, and bytes per sector (This is also referred to as the drive's geometry) quickly and reliably. This method involves reading the computer's BIOS drive table directly, after reading the drive type number from the CMOS area. This method allowed NetWare to get the drive geometry information consistently and reliably, and meant a standardization in the drives supported. Unfortunately, this method also imposed limitations--although these limitations would not be felt for years to come. All PC AT computers of the time were using the AT standard disk controller design. NetWare had no problems running on these drives since all the disks were formatted at 17 sectors per track and each sector contained 512 bytes of data. No drive had more than 1,024 cylinders (a limitation of the original AT BIOS), each track had no more than 63 sectors per track, and there were no more than 16 heads. As a result, all hard drives were limited to about 500MB, but that was considered more storage space than anyone would need. The largest drive supported by the BIOS drive type was only a 117MB drive (type 9 in the original AT BIOS). NetWare v2.0a worked fine in this framework for the first couple of years. But as newer and larger drives became available and as more drive manufacturers came out with hard drives that didn't directly support the BIOS drive table, users needed a product to use the increased capacity of these drives. Probably the best known option of the time was the Golden Bow ROM extension board. This board was a combination hardware/software solution: The hardware consisted of a BIOS drive table extension Read-Only Memory (ROM), and the software consisted of a patch for the operating system files and utilities so they would recognize the new ROM. The Golden Bow ROM extension board allowed for the use of more than 25 different drive types--most of which were specified by drive manufacturer and model. The extension board also allowed for the use of the then new RLL-encoded controllers for the AT bus. The RLL controller formatted disks to a consistent 26 sectors per track, thus increasing disk capacity by 50 percent. This option breathed life into NetWare v2.0a installations where disk space was tight and being limited by the BIOS drive tables on some computers was not acceptable. NetWare v2.0a also introduced the Novell disk coprocessor board (DCB), which was the first small computer system interface (SCSI) host board available to the NetWare world. The DCB allowed the use of the Adaptec 4000 and 4070 midstage controllers, which were standalone hard disk controller cards that connected a SCSI host either to an MFM disk (4000) or to a RLL (4070) certified ST-506. (ST-506 is the standard hard disk designation for drives attached to an AT-type controller.) The DCB allowed for the use of drives such as the Maxtor 1240, which formatted to 179MB on the Adaptec 4070, or the Maxtor 2190/Priam ID230 drives, which formatted to 240MB on the 4070. At the time, these were considered the largest drives available for the AT computers. Soon after the DCB was introduced, several embedded controller SCSI drive devices became available. The major difference between these drives and the Maxtor 1240/2190 was that the controller was directly attached to the SCSI hard drive. The embedded controller increased performance because the data and controller signals did not have to be passed over any cables longer than half an inch. Probably the most famous drive series of the time was the CDC Wren III series. NetWare v2.0a, however, still had some major limitations. It could only support drives on the AT controller that were specifically defined in BIOS, or drives that were connected to a DCB and defined in the NetWare DISKSET program. NetWare v2.0a had a drive limitation of 255MB. Drives larger than 255MB could only have a single NetWare partition of 255MB; the rest of the drive would be wasted. The 255MB limitation was overcome with the release of NetWare v2.1. The 17-sector limitation imposed on AT-type disk controllers was also lifted, making the way for the new technology of Enhanced Small Disk Interface (ESDI) drives. ESDI is an enhanced mode of RLL operation that allows hard disks to be formatted up to the theoretical limit of 63 sectors per track. The controllers could also work efficiently with drives that have more than 1,024 cylinders. Due to the limitations of the AT controller from the computer's BIOS, however, most of these controllers needed a driver to run correctly. Sector Translation answered this need. Sector Translation is a method whereby the controller, through the use of an intelligent BIOS, converts the hard drive's physical geometry into a compatible logical geometry by lowering the number of cylinders and increasing the number of heads and sectors per track. This process is done on the controller, and the controller takes care of the logistics of making the computer think the drive is the size defined in the CMOS/BIOS tables. Most drives use the BIOS drive type 1 to operate. NetWare v2.1 also introduced Value-Added Disk Drivers (VADDs). The VADD specification allowed any disk controller manufacturer to produce a driver for its interfaces to operate in a NetWare environment. (These drivers are similar to the drivers manufacturers produced for DOS.) NetWare was now open to all the available SCSI host adapters, which were starting to flood the PC marketplace. Users had a viable option to the DCB for their SCSI drive needs. With the release of NetWare v2.1, the limitation of one partition was lifted, and the ability to have multiple NetWare volumes on a single drive going beyond 255MB made superservers a workable option. A SCSI host adapter can control up to eight controllers, and each controller can support up to two drive devices. Using embedded controller drives limited the controller to only one drive. Soon the market was seeing the release of 300MB and 600MB hard drives for both the SCSI and ESDI interfaces. At this point, some of Novell's early decisions to stay within the constraints of the AT BIOS drive definition caused problems. The most obvious problem is referred to as Cylinder Wrap. The Cylinder Wrap is a condition that occurs when a drive's NetWare partition is set up with a DOS-compatible partitioning program (such as the partition definition routines in NETGEN's Custom option). Since the AT BIOS limit is 1,024 cylinders, NetWare can't interpret the cylinder request if a drive has a partition going beyond that limit. With a drive that has more than 1,024 cylinders, NetWare subtracts 1,024 from the requested cylinder and writes or reads from the remaining cylinder number. Cylinder Wrap also occurs when Hot Fix is activated due to a write fault. This possibility is worse than a write request because only one block in a file may be damaged, but you must scan all files to find that one block. In pursuit of complete compatibility, Novell has corrected this problem with special- purpose files and the strict instruction to use the default mode of NetWare installation to define the hard drive's partition table. What this means is that you must run through the NetWare Installation option from the NetGen menu twice. The first time selecting the Default Installation option, and going through the steps up to the point that the partition table is written to the disk. And the second time into the NetWare Installation choice selecting the Custom Installation option to define the volumes, number of directory entries, and other system parameters. Also when NetWare 386 was designed, the AT BIOS limitations were completely removed. The newest hard drives are the IDE drives developed by the Connor Corporation. Integrated Drive Electronics (IDE, developed by Connor Technologies) drives are similar to SCSI drives in that the controller for the drive is embedded on the drive itself, but IDE drives are also similar to ESDI drives in that they use the computers BIOS to function and allow for limited sector translation, and only two drives are supported in a single machine. These drives are particularly appealing to NetWare users because they have a fairly large capacity (200MB, with 500MB drives on the horizon) at a fairly low cost (approximately $1,000). Unfortunately, these drives have opened up a whole new arena of disk errors. Since these drives use a limited sector translation capability (which converts physical capacity to match a BIOS defined drive type of similar or lesser capacity), it is impossible to use the full capacity of the drives on most computers. This problem has two solutions: First, the CMOS user definable drive type allows you to specify a drive's geometry and force it into the computer's CMOS definitions directly from the keyboard. Unfortunately, since NetWare still relies on the computer's BIOS drive tables for the AT Standard and ISADISK drivers, the user definable drive types are unusable in a NetWare environment. The second solution is the disk preparation software package Disk Manager -N from On-Track Systems. This product prepares any AT Controller device for NetWare by putting a stamp on the drive and by modifying the Operating Ssytem and disk drivers for NetWare. This program not only allows for drive types that do not fit directly into the BIOS drive table, but also circumvents the 1,024 cylinder limitation. Many drive solutions are available today. With the advent of smaller physical drive sizes and the increase in magnetic media reliability, multi-gigabyte hard drives in a single 3.5" drive frame (all completely addressable by a NetWare server) are not too far off.