| Company / developer | Novell, Inc. |
|---|---|
| Working state | Current |
| Source model | Closed source |
| Initial release | 1983 |
| Latest stable release | 6.5 SP8 / May 6, 2009 |
| Available language(s) | English |
| Kernel type | Hybrid kernel |
| Default user interface | Command-line interface, Text user interface |
| License | Proprietary |
| Official website | www.novell.com |
NetWare is a network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, with network protocols based on the archetypal Xerox Network Systems stack.
Novell superseded NetWare with Open Enterprise Server (OES) in 2005. The latest version of NetWare is v6.5 Support Pack 8, which is identical to OES 2 SP1, NetWare Kernel.
NetWare evolved from a very simple concept: file sharing instead of disk sharing. In 1983 when the first versions of NetWare originated, all other competing products were based on the concept of providing shared direct disk access. Novell's alternative approach was validated by IBM in 1984, which helped promote the NetWare product.
Novell NetWare shared disk-space in the form of NetWare volumes, comparable to DOS volumes. Clients running MS-DOS would run a special terminate and stay resident (TSR) program that allowed them to map a local drive letter to a NetWare volume. Clients had to log in to a server in order to be allowed to map volumes, and access could be restricted according to the login name. Similarly, they could connect to shared printers on the dedicated server, and print as if the printer was connected locally.
At the end of the 1990s, with Internet connectivity booming, the Internet's TCP/IP protocol became dominant on LANs. Novell had introduced limited TCP/IP support in NetWare v3.x (circa 1992) and v4.x (circa 1995), consisting mainly of FTP services and UNIX-style LPR/LPD printing (available in NetWare v3.x), and a Novell-developed webserver (in NetWare v4.x). Native TCP/IP support for the client file and print services normally associated with NetWare was introduced in NetWare v5.0 (released in 1998).
During the early-to-mid 1980s Microsoft introduced their own LAN system in LAN Manager, based on the competing NBF protocol. Early attempts to muscle in on NetWare failed, but this changed with the inclusion of improved networking support in Windows for Workgroups, and then the hugely successful Windows NT and Windows 95. NT, in particular, offered services similar to those offered by NetWare, but on a system that could also be used on a desktop, and connected directly to other Windows desktops where NBF was now almost universal.
The popular use and growth of Novell NetWare began in 1985 with the simultaneous release of NetWare 286 2.0a and the Intel 80286 16-bit processor. The 80286 CPU featured a new 16-bit protected mode that provided access to up to 16 MB RAM as well as new mechanisms to aid multi-tasking. (Prior to the 80286, PC CPU servers used the Intel 8086/8088 8/16-bit processors, which were limited to an address space of 1MB with not more than 640 KB of directly addressable RAM.)
The combination of a higher 16 MB RAM limit, 80286 processor feature utilization, and 256 MB NetWare volume size limit (compared to the 32 MB that MS-DOS allowed at that time) allowed the building of reliable, cost-effective server-based local area networks for the first time. The 16 MB RAM limit was especially important, since it made enough RAM available for disk caching to significantly improve performance. This became the key to Novell's performance while also allowing larger networks to be built.
In another significant innovation, NetWare 286 was hardware-independent, unlike competing server systems from 3Com. Novell servers could be assembled using any brand system with an Intel 80286 or higher CPU, any MFM, RLL, ESDI, or SCSI hard drive and any 8- or 16-bit network adapter for which NetWare drivers were available.
Novell also designed a compact and simple DOS-client software program that allowed DOS stations to connect to a server and access the shared-server hard drive. While the NetWare server file system introduced a new, proprietary file-system design, it looked like a standard DOS volume to the workstation, ensuring compatibility with all existing DOS programs.
NetWare originated from consulting work by SuperSet Software, a group founded by the friends Drew Major, Dale Neibaur, Kyle Powell and later Mark Hurst. This work stemmed from their classwork at Brigham Young University in Provo, Utah, starting in October 1981.
In 1983, Raymond Noorda engaged the work by the SuperSet team. The team was originally assigned to create a CP/M disk sharing system to help network the CP/M hardware that Novell sold at the time. The team was privately convinced that CP/M was a doomed platform and instead came up with a successful file-sharing system for the newly introduced IBM-compatible PC. They also wrote an application called Snipes - a text-mode game - and used it to test the new network and demonstrate its capabilities. Snipes was the first network application ever written for a commercial personal computer, and it is recognized as one of the precursors of many popular multiplayer games such as Doom and Quake.[1]
This network operating system (NOS) was later called Novell NetWare. NetWare was based on the NetWare Core Protocol (NCP), which is a packet-based protocol that enables a client to send requests to and receive replies from a NetWare server. Initially NCP was directly tied to the IPX/SPX protocol, and NetWare communicated natively using only IPX/SPX.
The first product to bear the NetWare name was released in 1983. It was called NetWare 68 (aka S-Net); it ran on the Motorola 68000 processor on a proprietary Novell-built file server and used a star network topology. This was soon joined by NetWare 86 V4.x, which was written for the Intel 8086. This was replaced in 1985 with Advanced NetWare 86 version 1.0a which allowed more than one server on the same network. In 1986, after the Intel 80286 processor became available, Novell released Advanced NetWare 286 V1.0a and subsequently V2.0B (that used IPX routing to allow up to 4 network cards in a server). In 1989, with the Intel 80386 available, Novell released NetWare 386. Later Novell consolidated the numbering of their NetWare releases, with NetWare 386 becoming NetWare 3.x.
NetWare version 2 had a reputation as notoriously difficult to configure, since the operating system was provided as a set of compiled object modules that required configuration and linking. Compounding this inconvenience was that the process was designed to run from multiple diskettes, which was slow and unreliable. Any change to the operating system required a re-linking of the kernel and a reboot of the system, requiring at least 20 diskette swaps. An additional complication in early versions was that the installation contained a proprietary low-level format program for MFM hard drives, which was run automatically before the software could be loaded, called COMPSURF.
NetWare was administered using text-based utilities such as SYSCON. The file system used by NetWare 2 was NetWare File System 286, or NWFS 286, supporting volumes of up to 256 MB. NetWare 286 recognized 80286 protected mode, extending NetWare's support of RAM from 1 MB to the full 16 MB addressable by the 80286. A minimum of 2 MB was required to start up the operating system; any additional RAM was used for FAT, DET and file caching. Since 16-bit protected mode was implemented the i80286 and every subsequent Intel x86 processor, NetWare 286 version 2.x would run on any 80286 or later compatible processor.
NetWare 2 implemented a number of features inspired by mainframe and minicomputer systems that were not available in other operating systems of the day. The System Fault Tolerance (SFT) features included standard read-after-write verification (SFT-I) with on-the-fly bad block re-mapping (at the time, disks did not have that feature built in) and software RAID1 (disk mirroring, SFT-II). The Transaction Tracking System (TTS) optionally protected files against incomplete updates. For single files, this required only a file attribute to be set. Transactions over multiple files and controlled roll-backs were possible by programming to the TTS API.
NetWare 286 2.x supported two modes of operation: dedicated and non-dedicated. In dedicated mode, the server used DOS only as a boot loader to execute the operating system file net$os.exe. All memory was allocated to NetWare; no DOS ran on the server. For non-dedicated operation, DOS 3.3 or higher would remain in memory, and the processor would time-slice between the DOS and NetWare programs, allowing the server computer to be used simultaneously as a network file-server and as a user workstation. All extended memory (RAM above 1 MB) was allocated to NetWare, so DOS was limited to only 640kB; expanded memory managers that used the MMU of 80386 and higher processors, such as EMM386, would not work either, because NetWare 286 had control of protected mode and the upper RAM, both of which were required for DOS to use this approach to expanded memory; 8086-style expanded memory on dedicated plug-in cards was possible however. Time slicing was accomplished using the keyboard interrupt. This feature required strict compliance with the IBM PC design model, otherwise performance was affected. Non-dedicated NetWare was popular on small networks, although it was more susceptible to lockups due to DOS program problems. In some implementations, users would experience significant network slowdown when someone was using the console as a workstation. NetWare 386 3.x and later supported only dedicated operation.
Server licensing on early versions of NetWare 286 was accomplished by using a key card. The key card was designed for an 8-bit ISA bus, and had a serial number encoded on a ROM chip. The serial number had to match the serial number of the NetWare software running on the server. To broaden the hardware base, particularly to machines using the IBM MCA bus, later versions of NetWare 2.x did not require the key card; serialised license floppy disks were used in place of the key cards.
Starting with NetWare 3.x, support for 32-bit protected mode was added, eliminating the 16 MB memory limit of NetWare 286. This allowed larger hard drives to be supported, since NetWare 3.x cached (copied) the entire file allocation table (FAT) and directory entry table (DET) into memory for improved performance.
By accident or design, the initial releases of the client TSR programs modified the high 16 bits of the 32-bit 80386 registers, making them unusable by any other program until this was fixed. Phil Katz noticed the problem and added a switch to his PKZIP suite of programs to enable 32-bit register use only when the NetWare TSRs were not present.
NetWare version 3 eased development and administration by modularization. Each functionality was controlled by a software module called a NetWare Loadable Module (NLM) loaded either at startup or when it was needed. It was then possible to add functionality such as anti-virus software, backup software, database and web servers, long name support (standard filenames were limited to 8 characters plus a three letter extension, matching MS-DOS) or Macintosh style files.
NetWare continued to be administered using console-based utilities. The file system introduced by NetWare 3.x and used by default until NetWare 5.x was NetWare File System 386, or NWFS 386, which significantly extended volume capacity (1 TB, 4 GB files) and could handle up to 16 volume segments spanning multiple physical disk drives. Volume segments could be added while the server was in use and the volume was mounted, allowing a server to be expanded without interruption.
Initially, NetWare used Bindery services for authentication. This was a stand-alone database system where all user access and security data resided individually on each server. When an infrastructure contained more than one server, users had to log-in to each of them individually, and each server had to be configured with the list of all allowed users.
The "NetWare Name Services" product allowed user data to be extended across multiple servers, and the Windows "Domain" concept is functionally equivalent to NetWare v3.x Bindery services with NetWare Name Services added on (e.g. a 2-dimensional database, with a flat namespace and a static schema).
For a while, Novell also marketed an OEM version of NetWare 3, called Portable NetWare, together with OEMs such as Hewlett-Packard, DEC and Data General, who ported Novell source code to run on top of their Unix operating systems. Portable NetWare did not sell well.
While NetWare 3.x was current, Novell introduced its first high-availability clustering system, named NetWare SFT-III, which allowed a logical server to be completely mirrored to a separate physical machine. Implemented as a shared-nothing cluster, under SFT-III the OS was logically split into an interrupt-driven I/O engine and the event-driven OS core. The I/O engines serialized their interrupts (disk, network etc.) into a combined event stream that was fed to two identical copies of the system engine through a fast (typically 100 Mbit/s) inter-server link. Because of its non-preemptive nature, the OS core, stripped of non-deterministic I/O, behaves deterministically, like a large finite state machine.
The outputs of the two system engines were compared to ensure proper operation, and two copies fed back to the I/O engines. Using the existing SFT-II software RAID functionality present in the core, disks could be mirrored between the two machines without special hardware. The two machines could be separated as far as the server-to-server link would permit. In case of a server or disk failure, the surviving server could take over client sessions transparently after a short pause since it had full state information and did not, for example, have to re-mount the volumes - a process at which NetWare was notoriously slow. SFT-III was the first NetWare version able to make use of SMP hardware - the I/O engine could optionally be run on its own CPU. The modern incarnation of NetWare's clustering, Novell Cluster Services (introduced in NetWare v5.0), is very different from SFT-III. NetWare SFT-III, ahead of its time in several ways, was a mixed success.
Novell designed NetWare 386 3.x to run all applications on the server at the same level of processor memory protection, known as "ring 0". While this provided the best possible performance, it sacrificed reliability. The result was that crashes (known as abends, short for abnormal ends) were possible and would result in stopping the system. Starting with NetWare 5.x, software modules (NetWare Loadable Modules or NLM's) could be assigned to run in different processor protection rings, ensuring that a software error would not crash the system.
Version 4 in 1993 also introduced NetWare Directory Services, later re-branded as Novell Directory Services (NDS), based on X.500, which replaced the Bindery with a global directory service, in which the infrastructure was described and managed in a single place. Additionally, NDS provided an extensible schema, allowing the introduction of new object types. This allowed a single user authentication to NDS to govern access to any server in the directory tree structure. Users could therefore access network resources no matter on which server they resided, although user license counts were still tied to individual servers. (Large enterprises could opt for a license model giving them essentially unlimited per-server users if they let Novell audit their total user count)
Version 4 also introduced a number of useful tools and features, such as transparent compression at file system level and RSA public/private encryption.
Another new feature was the NetWare Asynchronous Services Interface (NASI). It allowed network sharing of multiple serial devices, such as modems. Client port redirection occurred via an MS-DOS or Microsoft Windows driver allowing companies to consolidate modems and analog phone lines.[2]
The upgrade was not without its flaws- initially NetWare 4 could not coexist with earlier versions on the same network because of incompatibilities.[3]
Promised as early as 1988, when the Microsoft-IBM collaboration was still ongoing and Microsoft OS/2 was still a fairly limited 16-bit product,[4] the product didn´t become commercially available until IBM and Microsoft had parted ways and IBM had turned OS/2 into a 32-bit, pre-emptive multitasking and multithreading OS.
By August, 1993 [5] Novell released its first version of "Netware for OS/2". This first release supported OS/2 2.1 (1993) as the base OS, and required that users first buy and install IBM OS/2, then purchase NetWare 4.01, and then install the NetWare for OS/2 product. It retailed for $200. [6]
By around 1995, and coincidental with IBM´s renewed marketing push for its 32-bit OS/2 Warp OS, both as a desktop client and as a LAN server (OS/2 Warp Server), NetWare for OS/2 began receiving some good press coverage. "NetWare 4.1 for OS/2" allowed to run Novell´s network stack and server modules on top of IBM´s 32-bit kernel and network stack. It was basically NetWare 4.x running as a service on top of OS/2. It was compatible with third party client and server utilities and NetWare Loadable Modules [1].
Since IBM´s 32-bit OS/2 included Netbios, IPX/SPX and TCP/IP support, this means that sysadmins could run all three most popular network stacks on a single box, and use the OS/2 box as a workstation too. NetWare for OS/2 shared memory on the system with OS/2 seamlessly. The book "Client Server survival Guide with OS/2" described it as "glue code that lets the unmodified NetWare 4.x server program think it owns all resources on a OS/2 system". It also claimed that a NetWare server running on top of OS/2 only suffered a 5% to 10% overhead over NetWare running over the bare metal hardware, while gaining OS/2´s pre-emptive multitasking and object oriented GUI. [7]
Novell continued releasing bugfixes and updates to NetWare for OS/2 up to 1998 [8]
Novell's strategy with NetWare 286 2.x and 3.x proved very successful; before the arrival of Windows NT Server, Novell claimed 90% of the market for PC based servers.
While the design of NetWare 3.x and later involved a DOS partition to load NetWare server files, this feature became a liability as new users preferred the Windows graphical interface to learning DOS commands necessary to build and control a NetWare server. Novell could have eliminated this technical liability by retaining the design of NetWare 286, which installed the server file into a Novell partition and allowed the server to boot from the Novell partition without creating a bootable DOS partition. Novell finally added support for this in a Support Pack for NetWare 6.5.
As Novell used IPX/SPX instead of TCP/IP, they were poorly positioned to take advantage of the Internet in 1995. This resulted in Novell servers being bypassed for routing and Internet access in favor of hardware routers, Unix-based operating systems such as FreeBSD, and SOCKS and HTTP Proxy Servers on Windows and other operating systems.
Novell priced NetWare 4.10 similarly to NetWare 3.12, allowing customers who resisted NDS (typically small businesses) to try it at no cost.
Later Novell released NetWare version 4.11 in 1996 which included many enhancements that made the operating system easier to install, easier to operate, faster, and more stable. It also included the first full 32-bit client for Microsoft Windows-based workstations, SMP support and the NetWare Administrator (NWADMIN or NWADMN32), a GUI-based administration tool for NetWare. Previous administration tools used the Cworthy interface, the character-based GUI tools such as SYSCON and PCONSOLE with blue text-based background. Some of these tools survive to this day, for instance MONITOR.NLM.
Novell packaged NetWare 4.11 with its Web server, TCP/IP support and the Netscape browser into a bundle dubbed IntranetWare (also written as intraNetWare). A version designed for networks of 25 or fewer users was named IntranetWare for Small Business and contained a limited version of NDS and tried to simplify NDS administration. The intranetWare name was dropped in NetWare 5.
During this time Novell also began to leverage its directory service, NDS, by tying their other products into the directory. Their e-mail system, GroupWise, was integrated with NDS, and Novell released many other directory-enabled products such as ZENworks and BorderManager.
NetWare still required IPX/SPX as NCP used it, but Novell started to acknowledge the demand for TCP/IP with NetWare 4.11 by including tools and utilities that made it easier to create intranets and link networks to the Internet. Novell bundled tools, such as the IPX/IP gateway, to ease the connection between IPX workstations and IP networks. It also began integrating Internet technologies and support through features such as a natively hosted web server.
With the release of NetWare 5 in October 1998, Novell switched its primary NCP interface from the IPX/SPX network protocol to TCP/IP to meet consumer demands.[9] IPX/SPX was still supported, but the emphasis shifted to TCP/IP. Novell also added a GUI to NetWare. Other new features were:
The Cluster Services greatly improved on SFT-III, as NCS did not require specialized hardware or identical server configurations.
NetWare 5 was released during a time when NetWare market share dropped precipitously; many companies and organizations were replacing their NetWare servers with servers running Microsoft's Windows NT operating system.
Around this time, Novell also released their last upgrade to the NetWare 4 operating system, NetWare 4.2.
NetWare 5 and above supported Novell NetStorage for Internet-based access to files stored within NetWare.[10][11]
Novell released NetWare 5.1 in January 2000. It introduced a number of useful tools, such as:
NetWare 6 was released in October 2001, shortly after its predecessor. This version has a simplified licensing scheme based on users, not servers. This allows unlimited connections per user. Novell Cluster Services was also improved to support 32-node clusters; the base NetWare 6.0 product included a two-node clustering license.
NetWare 6.5 was released in August 2003. Some of the new features in this version included:
The latest - and apparently last - Service Pack for NetWare 6.5 is SP8, released October 2008.
In 2003, Novell announced the successor product to NetWare: Open Enterprise Server (OES). First released in March 2005, OES completes the separation of the services traditionally associated with NetWare (such as Directory Services, and file-and-print) from the platform underlying the delivery of those services. OES is essentially a set of applications (eDirectory, NetWare Core Protocol services, iPrint, etc.) that can run atop either a Linux or a NetWare kernel platform. Clustered OES implementations can even migrate services from Linux to NetWare and back again, making Novell one of the very few vendors to offer a multi-platform clustering solution.
Consequent to Novell's acquisitions of Ximian and SuSE, a German Linux distributor, it is widely observed that Novell is moving away from NetWare and shifting its focus towards Linux. Much recent marketing seems to be focussed on getting faithful NetWare users to move to the Linux platform in future releases.[12] The clearest indication of this direction is Novell's controversial decision to release Open Enterprise Server in Linux form only. Novell later watered down this decision and stated that NetWare's 90 million users would be supported until at least 2015.[13] Meanwhile, many former NetWare customers rejected Novell's Linux efforts for other distributions like Red Hat.[14] Some of Novell's NetWare supporters have taken it upon themselves to petition Novell to keep NetWare in development.[15]
OES 2 was released on October 8, 2007. It includes NetWare 6.5 SP7, which supports running as a paravirtualized guest inside the Xen hypervisor and new Linux based version using SLES10.
As of 2010[update] some organizations still use Novell NetWare, but its ongoing decline in popularity began in the mid-1990s, when NetWare was the de facto standard for file and print software for the Intel x86 server platform. Modern (2009) NetWare and OES installations are used by larger organizations that may need the added flexibility they provide.
Microsoft successfully shifted market share away from NetWare products toward their own in the late-1990s.[16][17] Microsoft's more aggressive marketing was aimed directly to management through major magazines; Novell NetWare's was through IT specialist magazines with distribution limited to select IT personnel.
Novell did not adapt their pricing structure accordingly and NetWare sales suffered at the hands of those corporate decision makers[18] whose valuation was based on initial licensing fees. As a result, organizations that still use NetWare, eDirectory, and Novell software often have a hybrid infrastructure of NetWare, Linux, and Windows servers.
Novell introduced NetWare ELS (for Entry Level System) in 1987. In 1991 Novell introduced a radically different and cheaper product, NetWare Lite 1.0 (NWL),[19][20] in answer to Artisoft's similar LANtastic. Both were peer-to-peer systems, where no specialist server was required, but instead all PCs on the network could share their resources.
The product was upgraded to NetWare Lite 1.1 and also came bundled with some issues of DR DOS 6.0. Some components of NetWare Lite were used in Novell's NetWare PalmDOS 1 in 1992.
Significantly reworked, the product line became Personal NetWare 1.0 (PNW) in 1993. The ODI/VLM (for Open Datalink Interface) 16-bit DOS client portion of the drivers now supported individually loadable VLMs for an improved flexibility and customizability, whereas the server portion could utilize Novell's DPMS (DOS Protected Mode Services), if loaded, to reduce its conventional memory footprint and run in extended memory and protected mode. The NetWare Lite disk cache NLCACHE had been reworked into NWCACHE, which was easier to set up and could utilize DPMS as well, thereby reducing the DOS memory footprint and significantly speeding up disk performance. Personal NetWare came bundled with the network-enabled game NetWars 2.06.
The Personal NetWare 1.0 product saw five maintenance upgrades as well as various comprehensive updates to the corresponding VLM client driver suite (1.0, 1.1, 1.20, 1.21) as part of the Novell Client Kit for DOS & Windows up to November 1996, which added many new MLID (Media Link Interface Driver) drivers, including drivers for SLIP and PPP, as well as extra codepages and languages.
A full version of Personal NetWare (save the interactive tutorials) also came bundled with Novell DOS 7 in 1993/1994 at a price similar to that of the stand-alone version of Personal NetWare. Portions of Personal NetWare were incorporated into Novell's NetWare Mobile for DOS and LAN Workplace for DOS products, and as such compatible TCP/IP drivers became available for the system as well. Later, Personal NetWare was bundled with full versions of Caldera OpenDOS 7.01, DR-DOS 7.02 and 7.03 between 1997 and 1999, however, these bundles were delivered with the same Personal NetWare files shipping with Novell DOS 7, not the upgraded files, which had been made available for download by Novell since 1994. The ODI/VLM client stack with TCP/IP drivers also found its way into the DR-WebSpyder distribution.
When Novell in 1996 introduced its ODI32/NIOS 32-bit DOS/Windows client (Client32), it used NLM instead of VLM modules. While the NIOS client could reduce the conventional memory footprint downto 2 to 5 KB in total, the lack of something like a "PNW.NLM" module (in analogy to the VLM client's PNW.VLM) made it impossible to use the new client in conjunction with a Personal NetWare server.
NetWare dominated the network operating system (NOS) market from the mid-1980s through the mid- to late-1990s due to its extremely high performance relative to other NOS technologies. Most benchmarks during this period demonstrated a 5:1 to 10:1 performance advantage over products from Microsoft, Banyan, and others. One noteworthy benchmark pitted NetWare 3.x running NFS services over TCP/IP (not NetWare's native IPX protocol) against a dedicated Auspex NFS server and a SCO Unix server running NFS service. NetWare NFS outperformed both 'native' NFS systems and claimed a 2:1 performance advantage over SCO Unix NFS on the same hardware.
The reasons for NetWare's performance advantage are given below.
When first developed, nearly all LAN storage was based on the disk server model. This meant that if a client computer wanted to read a particular block from a particular file it would have to issue the following requests across the relatively slow LAN:
NetWare, since it was based on a file service model, interacted with the client at the file API level:
All of the work of searching the directory to figure out where the desired data was physically located on the disk was performed at high speed locally on the server. By the mid-1980s, most NOS products had shifted from the disk service to the file service model. Today, the disk service model is making a comeback, see SAN.
From the start, the NetWare design focused on servers with copious amounts of RAM. The entire file allocation table (FAT) was read into RAM when a volume was mounted, thereby requiring a minimum amount of RAM proportional to online disk space; adding a disk to a server would often require a RAM upgrade as well. Unlike most competing network operating systems prior to Windows NT, NetWare automatically used all otherwise unused RAM for caching active files, employing delayed write-backs to facilitate re-ordering of disk requests (elevator seeks). An unexpected shutdown could therefore corrupt data, making an uninterruptible power supply practically a mandatory part of a server installation.
The default dirty cache delay time was fixed at 2.2 seconds in NetWare 286 versions 2.x. Starting with NetWare 386 3.x, the dirty disk cache delay time and dirty directory cache delay time settings controlled the amount of time the server would cache changed ("dirty") data before saving (flushing) the data to a hard drive. The default setting of 3.3 seconds could be decreased to 0.5 seconds but not reduced to zero, while the maximum delay was 10 seconds. The option to increase the cache delay to 10 seconds provided a significant performance boost. Windows 2000 and 2003 server do not allow adjustment to the cache delay time. Instead, they use an algorithm that adjusts cache delay.
Most network protocols in use at the time NetWare was developed didn't trust the network to deliver messages. A typical client file read would work something like this:
In contrast, NCP was based on the idea that networks worked perfectly most of the time, so the reply to a request served as the acknowledgement. Here is an example of a client read request using this model:
All requests contained a sequence number, so if the client didn't receive a response within an appropriate amount of time it would re-send the request with the same sequence number. If the server had already processed the request it would resend the cached response, if it had not yet had time to process the request it would only send a "positive acknowledgement". The bottom line to this 'trust the network' approach was a 2/3 reduction in network transactions and the associated latency.
One of the raging debates of the 90s was whether it was more appropriate for network file service to be performed by a software layer running on top of a general purpose operating system, or by a special purpose operating system. NetWare was a special purpose operating system, not a timesharing OS. It was written from the ground up as a platform for client-server processing services. Initially it focused on file and print services, but later demonstrated its flexibility by running database, email, web and other services as well. It also performed efficiently as a router, supporting IPX, TCP/IP, and Appletalk, though it never offered the flexibility of a 'hardware' router.
In 4.x and earlier versions, NetWare did not support preemption, virtual memory,[21] graphical user interfaces, etc. Processes and services running under the NetWare OS were expected to be cooperative, that is to process a request and return control to the OS in a timely fashion. On the down side, this trust of application processes to manage themselves could lead to a misbehaving application bringing down the server.
By comparison, general-purpose operating systems such as Unix or Microsoft Windows were based on an interactive, time-sharing model where competing programs would consume all available resources if not held in check by the operating system. Such environments operated by preemption, memory virtualization, etc., generating significant overhead because there were never enough resources to do everything every application desired. These systems improved over time as network services shed their “application” stigma and moved deeper into the kernel of the “general purpose” OS, but they never equaled the efficiency of NetWare.
Probably the single greatest reason for Novell's success during the '80s and '90s was the efficiency of NetWare compared to general purpose operating systems. However, as microprocessors increased in power, efficiency became less and less of an issue. With the introduction of the Pentium processor, NetWare's performance advantage began to be outweighed by the complexity of managing and developing applications for the NetWare environment.
|
|||||||||||||||||||||||