Shared LAN Cache Datasheet

Features

Improves Performance

250% Increase in LAN Performance
10-50x Faster Data Reads Across WANs
Solution for Poor Segment Performance
Turbocharges slow file servers

Easy To Use

No Configuration or Setup Requires
Self-Maintaining Architecture
Transparent Operation

Compatible With All NOSs

Novell Netware 2.x, 3.x and 4.x
Microsoft NT Server/LAN Manager
DEC PathWorks
Unix NFS
Banyan Vines

General Description

Shared LAN Cache (patent pending) is a new LAN caching technology that significantly improves the performance of LAN and WAN file access. The technology enhances the performance of existing file servers by off-loading the overhead of reading data from existing file servers to Shared LAN Cache Servers.

Shared LAN Cache (SLC) addresses the increased performance required as application software, imaging and other large files are moved from local PC hard disks to file servers across LANs and WANs. Shared LAN Cache is easy to use and requires no user configuration or setup. All file security, rights, access methods and application metering work without modification.

SLC Improves Performance

Shared LAN Cache improves the performance of workstations reading data from file servers on LANs and WANs. SLC elevates the performance of file servers running NFS, Vines, LAN Manager, NT Server and DEC's PathWorks, enabling them to perform competitively with Novell's NetWare products. For Novell, SLC turbocharges existing file servers and overcomes many of the performance limitations of WANs and routers by providing both shared and local LAN caching.

Shared LAN Cache rejuvenates old file server hardware and software. SLC provides an inexpensive solution to a wide range of LAN and WAN performance problems without having to replace existing equipment or wiring. SLC Servers can also be used to dramatically enhance the performance of wireless LANs.

SLC Architecture

SLC redefines the traditional role of file servers by off-loading the task of binary data distribution to Shared LAN Cache Servers. These SLC Servers are distributed across LANs and WANs as required based on the level of caching and performance desired.

Shared LAN Cache utilizes an advanced client-server LAN caching architecture to solve LAN and WAN performance problems. SLC enhances the performance of LANs and WANs by providing a shared non- volatile cache on the local network segment. All of the SLC Clients on the local segment read cached data from SLC Server(s) off-loading existing file servers from redundant read requests.

SLC also supports a local caching option for the SLC Client to solve segment performance problems. This provides near-hard disk performance for application software running directly off of LANs or WANs.

Caching Concepts

The technology for caching memory, hard disks and CD ROMs has become a commodity technology now commonly bundled with operating systems. For example, memory caching is used extensively in microprocessor design to make up for the chasm between the speed of current CPUs and affordable memory systems. Likewise, hard disk or CD ROM caches use system memory to improve the performance of these relatively slow electromechanical storage devices.

Only recently have products appeared on the market that offer even limited support for LAN caching. They work like conventional caches, storing most recently used data in a local, memory-based cache. None of these products provide a non-volatile cache or a structure for sharing a cache with other nodes across a LAN; the unique and patent-pending technologies utilized in Shared LAN Cache™.

LAN Caching

Although many LANs were originally designed to handle databases and EMail, LANs are now being used for a much wider range of tasks; including shared user data, groupware, application software, imaging and electronic faxes. In spite of the additional demands, the problem of decreased LAN performance has not been addressed. This results in the common perception that LANs are slow.

LAN caching is similar in architecture to conventional hard disk or CD ROM caching except that the source of data is a Local Area Network. The SLC Client uses its local RAM and hard disk to cache data requested over a LAN from a file server. Since the LAN is typically much slower than the local disk/memory systems, caching data already read from the LAN significantly improves network performance.

WAN Caching

Wide Area Networks (WANs) allow workstations to access data from a remote file server, however WANs are much slower than LANs and have not been fully utilized.

Using an SLC Server to cache information from a WAN vastly improves performance by off-loading redundant data reads from the remote file server.

The first time data is requested from the remote file server, it is read by the SLC Client from that server and written into the SLC Server. Subsequent requests for the same data from any of the SLC Clients are satisfied by the SLC Server on the local LAN segment. The process is transparent to the workstation and the file server except for a remarkable (10-50X) improvement in performance.

SLC Client

The client portion of SLC is a small network redirector that is loaded on top of the existing network operating system shells on the client PC. The SLC Client software intercepts file Read and Write requests to the logical network file system and redirects some of these requests to the SLC Server.

File Open, Close and Lock requests are transmitted unchanged to the file server. Requests to read data, after permission to read the file has been granted by the file server, are then satisfied by the SLC Server. The SLC Client software determines where to read data depending upon the response times of the SLC Servers and the file server.

If the data is not found either in the local or the remote cache, the SLC Client reads the requested data from the file server and also transmits the data to the SLC Server. The transmission of data to the SLC Server occurs during the shadow of time when the client is waiting for new data from the file server and causes little degradation in performance.

SLC Server

The SLC Server provides a shared data cache that is accessed across a LAN. It is not a file server and all rights to access data in the shared cache must first be granted by the original file server. The SLC Server operates transparently to the existing file server, off-loading redundant data read requests.

Shared LAN Cache Servers can be configured with any combination of RAM and hard disk and require no administration or support. The SLC Server has no rights or privileges on the network. All of the data stored in the shared cache was originally read from the file server by SLC Clients and then written into the shared cache of the SLC Server.

SLC Operation

When an SLC Client first starts up, it broadcasts a request looking for an SLC Server. All of the SLC Servers respond with a performance benchmark based on their current loads and the SLC Client connects to the fastest SLC Server. This automatic load leveling removes any administration when multiple SLC Servers are located on the same LAN segment.

The SLC Server automatically ages data in the cache. As new data is written to the cache, and the cache fills up, data not recently accessed by the SLC Client is automatically discarded by the SLC Server. No setup or administration is required for this process.

Non-Volatile Cache

Both SLC Server and SLC Client employ a non-volatile cache that eliminates the need for redundant data read requests. While most caches in use today are volatile, losing their contents when power is removed, data in SLC’s non-volatile cache is retained and available immediately when power is applied.

The SLC Server employs non-volatile caching using flash memory or a high speed hard disk to preserve data when power is removed. The SLC Client software can also use a local, non-volatile cache to boost local segment performance.

Safe Caching

SLC Applications

LAN performance of 300-500 KBytes/sec is often considered to be acceptable for reading data from a LAN, however a number of network problems can keep users from achieving this level of performance. Even 500 KBytes/sec may not be adequate as application software places additional demands on LANs highlighting the need for Shared LAN Cache.

Poor segment performance due to old networking hardware including Arcnet (2Mb) or Token Ring (4Mb) presents a problem that can be economically addressed with the SLC Client local caching. This option automatically stores data in a local non-volatile cache. Using a local cache on the SLC Client reserves the limited bandwidth of the network segment for file writes and security requests to the file server.

Inter-segment delays caused by bridges and routers pose a second type of problem that can be solved by adding an SLC Server on the local segment. SLC Clients read data from an SLC Server located on the client side of the router. Delays that normally occur when data is read across a router are avoided because the data reads are re-directed to the SLC Server on the local segment.

Poor file server performance caused by either slow file server hardware or software is a third problem that can easily be overcome using an SLC Server. Shared LAN Cache Servers off-load existing file servers from redundant read requests for data. The SLC Server handles all of the requests for data reads (often 70-80% of the server load) enhancing performance and freeing up the file server for other tasks.

Shared vs. Client Caching

The SLC Client can be used in conjunction with an SLC Server or as a stand-alone product. With the local cache enabled, the SLC Client solves the problem of poor local segment performance by caching network data reads to a local non-volatile cache. Even a small 10-20 Megabyte local cache can eliminate most of the redundant reads to the network for an SLC Client running Windows and 3-4 application software packages.

Utilizing the SLC Server with a shared cache, however, is a better solution for reading data from remote file servers or WANs. Without the shared cache of an SLC Server, each SLC Client would have to go out across the WAN to read and cache the data. Using an SLC Server, data is only read once across the WAN and is written into an SLC Server where it is available to all of the SLC Clients.

An additional advantage of using SLC Servers is that no hard disk space is required for the SLC Client cache. All of the caching is done on the SLC Server where over 500 MB of the most recently read data are stored in a shared non-volatile cache.

LAN Switches

LAN Switches (also known as multi-port bridges and/or fast routers) have become a very popular option for increasing the effective LAN bandwidth to the desktop. Switches provide a painless way to micro-segment existing networks by simply replacing existing hubs with Switches requiring no changes in the wiring.

SLC Servers deliver optimum performance when connected to the high speed port (ATM, FDDI, Fast Ethernet or 100VG-AnyLAN) of a Switch. Without upgrading to a Switch, the connection between the SLC Server and the existing hub, which by definition is a single segment, could become the performance bottleneck.

Documentation

Shared LAN Cache is supplied with a users manual that contains detailed information on the setup and use of the software. Information is also provided on how to identify and isolate performance bottlenecks on LANs and WANs.

Disclaimer

Information supplied by Measurement Techniques is believed to be reliable and accurate at the time of printing. No liability is assumed by Measurement Techniques for the use of this material nor for the suitability of its products for a particular application.

Support

For additional information regarding Shared LAN Cache, please consult your local sales representative listed below or contact MTI directly. Post sales application assistance is available directly from Measurement Techniques.

Warranty

Measurement Techniques, Inc. warrants its hardware to be free of defects in materials and workmanship for a period of one year from the date of purchase. Software media only is warranted for a period of 90 days from the date of purchase to be free of media defects.

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