Network Monitoring

The Simple Network Management Protocol (SNMP) and Remote Monitoring (RMON) protocol are powerful tools that can be used to manage a medium to large network. In a small LAN, such as in a home office, these capabilities are not needed. If a device such as a cable/DSL modem or router is not working, you will probably be able to determine that quickly. This applies also to your printer (it has run out of toner or ink), and your computer(s) (it hangs or crashes). However, when a network is spread out over a large geographical area, or when a large number of network devices and computers are on the network, these two protocols can be used with management consoles to help you diagnose problems remotely and gather statistical information about your network. SNMP and RMON also can help you spot trouble before it becomes a real problem.

SNMP basically collects data about computers and other devices on the network, and is used with a management console application to provide a central reporting station. RMON is similar to SNMP but supports additional features, especially on the remote devices. By choosing a good management station application, you can set up thresholds for certain events (such as network traffic, errors, and other statistical information) so that automatic alerts are issued to warn you when something is amiss.

SNMP and RMON are covered in greater detail in Chapter 49, "Network Testing and Analysis Tools." If you manage a large network, the central network management application that you use (such as HP OpenView or IBM's Tivoli suite of products) uses these protocols to obtain information from networked devices or, in the case of RMON, to set variables in the Management Information Base (MIB) of these devices.

Server and Workstation Backups

Did you ever lose your address book? Did you have another copy? If you use a PDA or a laptop instead, let's rephrase the question: Did you ever lose the data on your PC? Did you have a backup? Trivial as it might seem, this is about the most important point to be made in this chapter.

Nothing will save your neck more often than a good backup of all computer systems in your network. It doesn't matter whether you've spent hundreds of thousands of dollars (or even millions) getting state-of-the art RAID (Redundant Array of Independent Disk) disk arrays that have multiple copies of data stored on separate disks. Many financial institutions even have online mirroring of data between distant geographical sites to prevent a natural disaster from causing loss of data. However, no matter how well you prepare your online storage to be fully redundant, there are other reasons you should establish a good schedule of regular backups of all important data on the computer systems in your network.

It's a RAID!

Actually, when the concepts were first developed, RAID stood for Redundant Array of Inexpensive Disks. Obviously, the name has been changed because most disks used in large-scale RAID systems are anything but inexpensive! If you want to know more about RAID techniques, from simple disk mirroring to disk striping, and combinations of the two, visit these websites : http://SearchStorage.techtarget.com (search for "The Essential RAID Primer"); Advanced Computer and Network Corporation's "Get to Know RAID" tutorial: www.acnc.com/04_01_07.html ; and AAA Data Recovery's RAID Tutorial: www.aaa-datarecovery.com/raid_tutorial.htm . You'll find excellent documentation for the various flavors of RAID technology that have been developed. RAID supports ATE/IDE (also known as PATA), SATA, SCSI, and SAS drive technologies.

Also, when purchasing RAID solutions from a vendor, keep in mind that the buzzword "RAID" doesn't have to imply that the solution offered will protect your data. RAID is an overall encompassing term for several disk technologies. Some of these technologies are concerned with preserving multiple copies of data, such as disk mirroring, whereas others are concerned with fast read or write access, such as disk striping. Combinations of the two are usually employed in an environment that requires fast access to online storage with provisions for data protection.

Lastly, although RAID technology is usually covered in a hardware book, such as Scott Mueller's Upgrading and Repairing Servers , it is also mentioned in this book because of the importance it plays in today's larger networks. You will find a more detailed discussion of RAID in Chapter 11, "Network Attached Storage and Storage Area Networks."

For example, even if you use disk mirroring and other RAID techniques, what are you going to do if a meteor falls out of the sky and lands on your computer room? Boom! There go all your computers, your data, and, of course, a few operators. You can replace the computers and the operators (with a little training, of course), but can you replace the data?

There is one other technology that can help you out when entire storage systems fail at your local site. Storage Area Networks (SANs) can be used to replicate data between sites that are located several miles away. You can also connect SANs over much longer geographical distances (from coast to coast ) by channeling the SAN traffic through standard long-haul protocols such as ATM or Frame Relay. For more information about SANs, see Chapter 11.

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For a more practical reason to perform frequent, regular backups, just think of your users. When was the last time a user deleted a file (or worse yet, a directory of files) and asked you to restore it? Backups can protect you from more than just computer failures and natural or unnatural disastersdo you really trust all of your employees? Bad mistake. As the old saying goes, trust everyone but cut the cards first. In a large organization it's difficult to keep all employees happy. Some studies have shown that most of the damage inflicted on individual computers or networks is an "inside job." You need to protect your network from both internal and external problem sources.

Nothing can substitute for a good backup, short of a new job (job security tends to drop some if you lose months of corporate data or even a single day's worth, depending on your industry).

Backup MediaTape, Optical Storage, and Hard Disk

The standard mechanism used by most sites to create backups of computer data is magnetic tape. You'll find all sorts of tape backup devices, ranging from Travan cartridges to the more modern high-capacity Digital Linear Tape (DLT) cartridges. You might even still see the old-fashioned, reel-to-reel nine-track tape in some installation. However, you should choose the backup media based on several things:

Is the backup needed for the short or long term?
If a restore is necessary, can the backup media perform up to your expectations?
How expensive is the backup media?
Do you need to exchange data with other sites, such as companies that provide a disaster recovery hot site?

If you have data that is transient and you only need to recover your systems to a known state that doesn't go far back in time, you can use many kinds of backup media. Most likely, your choice will depend on the speed at which you want to create backups and the speed at which the data can be restored. In this case, tape is probably your best choice. High-speed magnetic tape solutions are available that can back up and restore many gigabytes per hour . Magnetic tape also is good for short-term to long-term storage, provided it is cared for properly as specified by its manufacturer. However, for long-term storage, be sure to pick media that can be used in standard devices. For example, nine-track tapes were used for a long time as the standard in the industry for computer backups. However, if you are required to keep backups for several years due to regulatory requirements, for example, be sure to also keep around tape drives that can be used to read back the data stored on those tapes.

Note

At one of my jobs, I once watched the company spend a large sum of money to transfer a large stock of old nine-track tapes to more modern DLT media. Occasionally, a tape was found that was unreadable; however, most of the data was recovered and is now sitting in storage awaiting the next expensive conversion. Government regulations!

For long-term storage, you really don't have much choice because technology is changing so fast. However, be sure to look for a backup technology that is from a reliable manufacturer, whom you expect to be in business for a few years to come.

In an emergency, the amount of time required to restore data from a backup can be more important than the amount of time it takes to create the backup in the first place.

For example, it might be possible to break a mirror set cleanly, use one of the mirrored disks to create a backup, and then re-create the mirror set using the software provided by your RAID subsystem. This allows your users to continue using the system with minimal interference from the backup process. If you use a disk-mirroring setup that uses three or more mirrored disks for each mirror set, you can still provide for fault-tolerance while the backup is being produced because multiple disks in the system contain copies of the current data.

Restoring data to a RAID subsystem might take longer than the backup, or it might proceed along at the same rapid pace, depending on the disk controllers, device firmware, and other factors. When choosing a backup solution, don't forget that you need to consider the opposite of the backup: the restore. You might purchase a high-tech, whiz-bang disk subsystem that supports many different levels of RAID techniques, including online backup. However, if restoring data to multiple disks takes significantly longer than restoring to a single disk, you might want to consider an alternative solution.

In case the absolute worst thing that can happen happensyour site is down, not just the computers, due to some disaster such as a fireyou must be sure that the backup media you have is compatible with the equipment you will use in a disaster-recovery scenario. This is easy to overlook when shopping around for an off-site, hot-site provider. In this kind of situation, don't take the vendor's word for it. Test it. Take your backup tapes to the hot site and perform a restore. Time the restore. Be sure the media you are using is compatible with the hot site, and be sure the tape drives (or other media drives) are fast enough to get you back up and running in a short time.

Magnetic tape is not the only backup method available today. You'll find a wide assortment of media, from magneto-optical discs to recordable CDs and DVDs. The problem with recordable (and rewritable) CDs and DVDs is that they are still extremely slow (even if you have one of the faster drives) when compared to the speed at which magnetic tape can be used, for both the backup and the restore process. That said, recordable CD and DVD technology offers a rather inexpensive method for backing up a small computer system used in a SOHO environment. Because hard disk drives are measured in units of gigabytes, and CD-R discs in megabytes, you should consider recordable CD technology only for situations such as a small office or home office in which you just need to put a small amount of data in offline storage for backup purposes. Recordable DVDs, however, offer 4.7 gigabytes ( single-layer ) or 8.5 gigabytes (double-layer) per disc, which makes them very suitable for larger backup jobs (though not for full hard-disk backups, for which tape drives remain the most ideal solution).

When using rewritable (RW) discs for backup purposes, you're utilizing a medium that can be added to, erased, and reused. You can do this with many of the popular CD and DVD- burner software packages on the market today (Nero Ultra Edition, Easy Media Creator, and so on). Microsoft Windows XP and Vista also include CD-burning technology built into the operating system. Note, however, that the software incorporated into Windows XP is not as easy to use as some third-party applications and, more significantly, does not support DVD media (DVD drives are handled as if they were CD-RW drives). With dual-layer (DL) rewritable DVD drives now available for under $100, it's easy and inexpensive to upgrade systems with CD-RW or single-layer rewritable DVD drives to the latest technology. Keep in mind that rewritable DVD drives also work with CD-R and CD-RW media and some rewritable DVD drives include backup software.

One of the fastest growing means of backing up data is the external hard disk. Many vendors make external hard disk drives that connect to a system via USB 2.0 or IEEE-1394a ports (some drives offer both interfaces). The newest external drives offer capacities up to 500GB, and most include backup software. Some even feature a one-touch system that automatically runs a backup at the touch of a button on the backup drive. By making backups with an external hard disk and then transferring older backups to DL DVD media, you have a solution for fast frequent backups and long-term storage of older data.

Backup Rotation Schedules

When you create backups, first determine what data needs to be backed up and how long it must be accessible for restore purposes. If you have a volatile environment in which data older than a few weeks or months is no longer of use, you won't need to keep tapes or other media in long-term storage. However, for most companies, it's important to be able to produce data from months if not years ago to meet financial or regulatory requirements. In this case, you should create a backup rotation schedule appropriate for your needs.

For example, you might perform a full backup of all the data on your systems each night. Or you might want to produce a full backup once a week, and then produce incremental backups during the weekthat is, back up only the files that have changed since the full backup. Using the combination of the full backup and the incremental backup media, you can restore the system to the state it was in at any of the backup points.

In this kind of situation, when the next full backup is performed, the incremental backups might no longer be needed. If that is the case, you can reuse the tapes. The rate at which tapes or other media can be reused is called the rotation schedule . A good generic policy (depending on your environment, of course) is to create a weekly backup of all data and perform incremental backups during the week. This allows you to schedule the full backup for a time (such as the weekend ) when it won't impact your users. The weekly incremental backup media can be reused during the next week if the next full backup is successful.

The full backups done on a weekly basis can be stored for a month and then reused. Additionally, you might want to keep one of the end-of-month full backups for long-term storage, depending on the nature of your applications.

The full/incremental backup method has been developed to help reduce the backup window . This term is used to refer to the time that is available to the backup program when users do not need to have access to the system. However, as storage requirements continue to increase, and because data access in many industries is now a round-the-clock requirement, there is another technology that can be useful in these situations. As mentioned earlier in this chapter, Storage Area Networks can be used to offload storage devices from servers. SANs solve many problems associated with the standard SCSI devices. First, SCSI is limited in the number of devices that can be attached to a SCSI bus, as well as the short distances that SCSI hardware can be used over. SANs allow you to connect storage devices, both disk and tape, over much longer distances without any reduction in the access time. SANs also can be used to offload the backup process from a server's CPU. The SAN can instead be used to back up disk drives to tape drives, with no intervention by the server(s) that use the SAN.

Whatever rotation schedule you decide to use for your backup media, be sure that it meets the needs of your users and the applications they use. In addition, you should implement some type of mechanismsuch as a database storing information about each tapeso that you can discard the tape after it has been reused a certain number of times. Magnetic tape does degrade with each usage, and can even deteriorate when stored in a place where such things as temperature and humidity exceed the limits recommended by the manufacturer.

Using barcodes, or simply labeling tapes using a serial numbering method, can enable you to identify each tape in the database, and you can update the database each time a tape is used. Barcoding is used as part of the tape-identification system used with autoloaders or tape libraries, but it's a good idea even if you manually insert tapes into your backup drive. When a tape has passed its recommended useful lifetime, zap it with some utility to make the data unreadable, and toss the tape into the trash. It is a good idea to have a company policy on the disposal of all materials (including printouts as well as tapes, among other things) for security purposes. Who is looking in your trash dumpster? Better to be safe than to give someone else valuable information about your company's data.

Off-Site Storage

The backup media is helpful only if it's safely stored as well. If you need to restore only a single file because a user has made a mistake and deleted it, having a tape stored in the computer room makes this a quick and easy job. Pop the tape in the tape drive, restore the file, and then call the user. However, storing backup tapes in the same place that you house your computers is not always such a good idea. For example, this might not help you in the event of some kind of disaster, such as a fire. Not only are your computers lost, but your backups are gone as well.

For important data, the backup media should be sent to an off-site storage location as soon as practical after the backup has finished. In this scenario, if a disaster strikes your site, your tapes are safely stored away at another site and you can use them to recover when you move to a hot site or when you replace the destroyed equipment.

That said, what constitutes off-site storage? You can use several different places for off-site storage, depending on your needs. Consider first how safe the storage site is. Second, consider the amount of time it takes to retrieve the backup media. Third, consider the expense involved. Some sites to consider:

Use a company whose business is to pick up, store, and deliver backup media. There are many companies in this business. You'll want to visit their storage site to be sure that the storage conditions are conducive to long-term storage of sensitive backup media. Test the promised restore-time window by requesting the retrieval of tapes now and then. Be sure that the site offers 24-hour access to your data.
If you employ the service of a hot site that can be used to re-create your computer system or network during a disaster, the hot-site vendor often can provide services for off-site storage of backup media. In this case, you can save time during an emergency because you won't have to retrieve the tapes from a third party when you activate the hot site.
If you are a large company, it might be practical to store your backup media at another company site. The odds of a disaster striking multiple sites at the same time should be taken into consideration, as well as the storage conditions at the other site. For example, if the sites are within close proximity, this might not be a good idea. A natural disaster such as a hurricane or flood might cause a disaster at both places. Consider also the expense in having to regularly send tapes to your other company site. It might be less expensive to pay a professional service to store your tapes than to have employees transferring tapes from one site to another.
Take the media or the external hard disk drive home and stick the backups under your bed. This is no joke. I once worked at a small company in which the system manager would take the monthly backup home and store it under her bed until the next month. Along the same lines, if you operate a small office at home, you might consider taking your weekly or monthly backup tape to a safety deposit box at your local bank for off-site storage. The point is to make sure that the data is stored away from the computer system so that you can reduce the odds of a disaster destroying both your systems and your backups.