Televaulting and LAN Backup
Gilbert Held Although tape backup and tape rotation to an offsite storage facility is a long-established disaster recovery technique, there are limitations associated with this method. These limitations include the costs of performing the backups, timing gaps between the creation and backup of the data, media rotation, and costs associated with off-site storage and retrieval. Although most organizations use tape backup for disaster recovery, it is not the only option. As an alternative, you might consider televaulting, which is the focus of this article. Introduction to Televaulting The term televaulting describes the transmission of organizational data to an offsite storage location. Similar to the use of disaster recovery sites, the televaulting destination can be operated by a service contractor or by your own organization. Although televaulting is a relatively recent method for the backup of LAN data, its origin can be traced to the mainframe. As mainframes became extensively used within financial and travel circles, the timing-gap risks associated with conventional backup were widely acknowledged. Recognizing the necessity of many organizations to automatically record and transfer record changes via telecommunications in realtime, several vendors introduced televaulting products for mainframes during the late 1970s and early 1980s. The extension of televaulting to LAN-based systems represents a logical progression. Televaulting Methods There are two basic televaulting methods you can consider - televaulting to another organizational location, or televaulting to a third party. The first method requires your organization to have multiple locations as well as appropriate equipment at the storage location. Additionally, the storage location should be situated at a reasonable distance from the televaulting location to minimize the potential of a disaster affecting both locations. When you televault to another organizational location, you can use any software product commensurate with its ability to support your server's operating system and your budget. In comparison, if you contract for the use of a third party televaulting facility, your televaulting software must be compatible with the software at the storage location. Features to Examine There are four key televaulting features you should examine in addition to the financial aspects of particular products. Those features are:
After a few hours of Web searching, I located several televaulting products that include support for different features. Figure 1 provides a summary of televaulting features that were located. Although I was able to locate televaulting backup methods based on the transmission of full and partial files, as well as differencing, I could not locate a program that would televault changes to records on a real-time basis. Thus, sys admins, network managers, and LAN administrators may not have the ability to televault changes to their data as the changes occur, a feature which in the past was used in a mainframe environment by large financial and travel reservation organizations. Although most products use the Lempel-Ziv-Welch or Huffman coding schemes, some products employ delta processing and token representation. Delta processing results in a file treated as a series of blocks that typically range between 512 and 32 kbytes, with the actual block size based on the total size of the file. Each block size is treated as a separate entity with its own cyclic redundancy check (CRC) character computed for the block. If the file's archive bit changes, instead of the entire file being televaulted, only those blocks whose CRCs changed are transferred. Thus, delta processing can significantly reduce the quantity of data required to be televaulted when a file is revised. Token representation recognizes the fact that in many organizations the same file resides on the disk of tens to hundreds or even thousands of employees. For example, consider how many copies of Word Perfect, Microsoft Word, Lotus 123, or Excel are on your organization's desktops. Instead of televaulting each file every time a full save is required, a program that supports token representation televaults one copy of each program and a token to indicate other occurrences of the same program. Although delta processing and token representation are not strictly data compression methods in the classical sense, they can significantly reduce the quantity of data to be televaulted. You should also pay close attention to the type of transmission facility supported by a particular televaulting product. Depending upon the operating rate of the transmission facility, the extent of changes to your organizational data, and the support of different backup methods and data compression, you may or may not be a candidate for televaulting. Data Change Versus Transmission Let's assume your organization's server has 2 Gbytes of data, with 300 Mbytes of records in files being changed on a daily basis. Let's further assume that the televaulting product you are considering is limited to performing full backups but operates as a separate computer attached to a LAN. This enables the televaulting computer to transfer the file at a LAN operating rate onto its own storage and then transmit the file at the operating rate of the transmission facility supported by the televaulted location. If that transmission facility is a dial-up ISDN connection operating at 128 kbps, you would then compute the time required to transfer the file and compare that time to the time intervals you wish to transfer that file or series of files throughout the day. In this example, a 300 Mbyte file or series of files would require:
300 Mbytes * 8 bits/byte = 18750 seconds The preceding time represents approximately 5.2 hours, without considering the effect of the protocol overhead used for transmission nor the potential of data compression to reduce the quantity of data to be transmitted. Without considering those factors, the approximate 5.2 hours of transmission time would preclude your organization from performing a backup moving the backup offsite more frequently than every 5.2 hours. If the televaulting software supports data compression and your files represent a conventional relational database or a similar type of non-compressed file, you can normally expect to achieve between a 2.5:1 and 3:1 data reduction through the use of data compression. Assuming the transmission protocol introduces a 20% overhead, the time range required to transmit the 300 Mbyte file or series of files would become:
((300 Mbytes/2.5) * 8 bits/byte) * 1.2 = 9000 seconds
using a compression ratio of 2.5:1, and
((300 Mbytes/3) * 8 bits/byte) * 1.2 = 7500 seconds
using a compression rate of 3:1. Based on the preceding you can reasonably expect a transmission time between 7500 and 9000 seconds, or approximately 2.08 and 2.5 hours. Now let's assume your televaulting software supports differencing backup operations where differencing permits only records changed since the last backup occurred. Depending upon the frequency of backups and the activity of your servers, you may need to transmit a thousand 500-byte records every hour, or 500 records every 30 minutes. In this situation, your 128 kbps ISDN dial-up connection to a televaulting location based on a 2.5:1 compression ratio and 20% protocol overhead would require:
((500 records*500 bytes/record/2.5) * 8 bits/byte)*1.2 = 6.25 seconds
Thus, a differencing backup capability would enable you to periodically televault changes. In addition, with transmission time significantly reduced, you would be able to reduce the cost of transmission, which can typically vary between $0.06 and $0.12 per minute for a 128 kbps ISDN connection. If the televaulting software you intend to use supports delta processing and token replacement, you may be able to achieve a compression ratio of 30:1 to 50:1 or more. However, the ability to achieve such ratios depends upon the type of televaulting operation to be performed (full or incremental saves) as well as the files and file changes that occur. The best way to estimate the potential effect of delta processing and token replacement is through one or more controlled tests. First, select the files that would represent a typical televaulting operation and note their total storage. By actually televaulting those files, you can note the time required per Mbyte and plan your televaulting operations accordingly. In addition to the use of ISDN, some televaulting software products permit you to use an existing Internet connection to access the vendor's data storage management service. If you have spare outbound transmission capability on your existing Internet connection, this feature could eliminate additional transmission charges. However, since most corporate data deserves protection, especially when transmitted via the Internet, you may want to examine the security features associated with televaulting software. Security Most televaulting products support the use of the Data Encryption Standard (DES) using a key provided by the user. To facilitate security at a data storage management service provider, televaulted information is normally stored in encrypted form. However, in the event your facility undergoes a traumatic event resulting in the partial or complete destruction of your facility, including your encryption key, you would be up the proverbial creek without a paddle. Thus, it is highly recommended that you store your encryption key at two or more locations. Other security features offered with televaulting software include the use of client authentication and randomized binary file storage. The use of client authentication restricts the ability of your competitor or a cracker to access the televaulted location and stored files. The use of randomized binary file storage results in the storage of televaulted data based on a randomizing algorithm such that files are stored without an associated recognizable file name and are distributed over two or more clusters. This technique results in the service provider's server appearing as a huge collection of randomly stored, unintelligent files. This should reduce the level of anxiety concerning the storage of corporate data at a data storage service provider that might also be responsible for storing data from your competitors. Summary Televaulting represents another weapon in the sys admin's arsenal against a data center disaster. Although televaulting provides a mechanism to move backup data offsite, it is not a complete solution to a disaster recovery plan. Thus, if your organization's facility is rendered inaccessible, you should have previously developed a disaster recovery plan that includes a mechanism for retrieving previously televaulted data based on the use of equipment from another location, a hot backup site, or a contract that enables you to obtain office space and equipment in an contingency situation. Although televaulting may not be the complete answer to your organization's disaster recovery plan, it deserves careful consideration as a mechanism for inclusion in that plan. For Further Reference Several organizations offer televaulting products either as a standalone software program or as a software program bundled as a data storage management service to provide backup of LAN servers and PC workstations to an offsite storage center. Contact information about products and data storage management services is given below:
Connected Corporation www.connected.com Connected Online Backup 508-270-000 Iron Mountain (Formerly Rimage Corp. Televaulting) 612-888-3852 NewStar Collaborative Technologies, Inc. XPress Backup Software 314-434-6600 D.S. Data Storage, Inc. DS-Televaulting data storage www.dstelevaulting.com management services 416-736-8111 TeleBackup www.telebackup.com TSinfoPRO software 403-270-3822 Vytal Net www.vytalvault.com Vytal Vault electronic vaulting system 800-490-VNET
About the Author
Gilbert Held is an award-winning author and lecturer. Gil has authored more than 40 books and 250 articles during the past 20 years. Some of Gil's recent books include Virtual LANs, High Speed LAN Switching, Enhancing LAN Performance 2ed., Ethernet Networks 3ed., The Complete Modem Reference 3ed., and Data and Image Compression 4ed., all published by John Wiley & Sons of New York and Chichester, England. Gil can be reached via electronic mail at 235-8068@mcimail.com.
|