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
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,
Server and Workstation
It's a RAID!
Actually, when the concepts were first developed, RAID stood for Redundant Array of
Disks. Obviously, the
Also, when purchasing RAID solutions from a vendor, keep in mind that the
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
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
For a more practical reason to perform frequent, regular backups, just think of your users. When was the last time a
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).
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,
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
At one of my jobs, I once watched the company
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
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 (
When using rewritable (RW) discs for backup purposes, you're
One of the
When you create backups, first determine what data needs to be
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
. 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
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
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
That said, what
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
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
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