Although tape backup has long been the leading solution for backing up servers, it might not be appropriate for your situation, particularly if you have a relatively small server hard disk or don't require automation. The following sections discuss the leading alternatives to tape backup:
After discussing these alternatives, we take a look at the limitations of these methods. Disk-to-Disk (D2D) BackupAs an alternative to tape backup, many users of desktop PCs and entry-level servers now use some form of D2D backup. The most common type of D2D backup involves the use of an external IEEE 1394 or USB 2.0based hard disk equipped with backup software. "One button" backup drives can start the backup program automatically as soon as the drive is plugged in to the system and powered up. For drives with relatively small amounts of changing data to back up, a low-end D2D backup using an external hard disk makes a great deal of sense. External hard disks are now available with capacities as high as 500GB. External drives with capacities of 300GB or larger are big enough to permit a full backup and many incremental backups of a typical 160GB entry-level server hard disk. Unlike tape backups, which require that the tape be advanced to a particular point before a restore process can begin, restorations from a D2D backup can begin instantaneously. D2D backup is not limited to USB 2.0 or IEEE 1394 drives, however. Network-based backup appliances are available for backing up multiple stations on a network. In addition to traditional backup programs that can also be used in a D2D backup process, special D2D software is now available from several sources. IBM introduced Tivoli Continuous Data Protection (CDP) for Files in 2005 for Windows 2000 Server, Windows XP, and Windows Server 2003. CDP backs up changed files to a variety of local and network drives in real-time and periodically backs up data to a remote file server or Tivoli Storage Manager. For more information, see www-306.ibm.com/software/tivoli/products/continuous-data-protection/. Microsoft also released System Center Data Protection Manager (DPM) D2D program in 2005. DPM supports Windows Server 2003 on servers or NAS storage devices. DPM tracks and stores byte-level changes to server files and offers scheduled replication. For more information, see www.microsoft.com/windowsserversystem/dpm/default.mspx. Traditional backup programs are also available in D2D versions.
High-end disk-based backup devices that emulate tape libraries are also available. These devices enable a backup to be performed directly to a large hard disk array. Later, backup files can be transferred to tape for archiving operations, enabling the backup drive to be reused. Iomega REVAlthough current tape technologies such as LTO, SDLT, and DAT 72 are much faster than their predecessors, tape drives are still hampered by their linear technology that requires sequential access to data. To find a particular area of a tape to use for backup or restoration, you must move the tape past the recording head. Even though some recent tape technologies store certain information about a particular cartridge in the cartridge's NVRAM, it still takes time to rewind the tape and advance it to a particular location. If only certain files need to be restored, the user must wait as the tape is advanced to the first file, the file is read and restored to disk, the tape is advanced to the next file, and so forth. To replace outdated files on a tape, the tape must be rewritten. In contrast, removable-media storage provides random, rather than sequential, access to files and easy replacement, when necessary, of outdated information. However, traditional removable-media storage such as Zip, rewritable CD, and even rewritable DVD do not have capacities comparable to even entry-level server hard disks. Iomega's REV removable-media drive is designed to provide capacity comparable to that of DAT 72 or DLT VS80 tape drives while providing faster read and write access. REV uses 35GB hard-disk-type removable-media cartridges that Iomega refers to as removable rigid disks (RRDs). Unlike older technologies such as Zip, REV's RRD cartridges provide a sealed, air-filtered environment for read/write heads and electronics. The RRD media in a REV cartridge spins at 4,200RPM. While this is significantly slower than desktop ATA/IDE hard disks, this spin rate is comparable to that of many laptop ATA/IDE hard disks. In drag-and-drop file transfer tests, REV drives offer comparable transfer rates to 30GB ATA/IDE hard disks with files up to 64KB in size, and they are much faster with files of 1MB or larger. The maximum data transfer is up to 25MBps. Iomega REV CapacityThe native capacity of any Iomega REV drive is 35GB. Iomega claims a maximum compressed capacity of 90GB (2.6:1), based on testing performed with the Calgary Corpus data set. However, most users will not see this level of data compression in most real-world operations. The reason is that the files used in the Calgary Corpus were primarily text files. As any time spent using PKZip, WinZip, or the built-in Zip-compatible Windows XP archiving feature will tell you, text files can be compressed up to 90% smaller than normal. However, a great deal of the data on today's systems is already compressed data, such as JPEG photos, PDF files, MP3 and WMA audio files, zip and cab archives, and so forth. A better estimate for compression performance is to assume a maximum capacity of 70GB (2:1 compression), as is assumed by most third-party backup products. Note The Calgary Corpus data set was developed in 1990 by Tim Bell and Ian Witten. It can be downloaded from www.data-compression.info/Corpora/CalgaryCorpus/. A newer data set used for compression testing is the Canterbury Corpus. It can be downloaded from http://corpus.canterbury.ac.nz/index.html. This corpus was developed in 1997. You might want to try both with your favorite backup or archiving programs to see how the results differ. Iomega REV DrivesIomega offers a wide variety of drive interfaces for REV, enabling you to choose a drive for almost any type of internal or external host adapter. Table 9.9 lists available models. Note that all drives include Iomega Automatic Backup Pro for Windows 2000 and XP.
REV is supported by many third-party server backup applications. To determine whether you need updates, you can visit your backup application vendor's website. Some vendors offer bundles including REV drives, media, and a backup application. Note that the NT Backup utility that is built in to Windows 2000 Server and Windows Server 2003 cannot span a backup to multiple REV cartridges unless Firestreamer-RM is installed.
Note For users of larger hard disks who need an autoloader, REV is also available in a 10-cartridge autoloader format. The REV Autoloader 1000 is a desktop device with a native capacity of 350GB and a compressed capacity of 700GB (2:1 compression). It includes CA BrightStor ARCServe Backup OEM edition for a single server, and it connects to a server via a 68-pin LVD SCSI connection. Options include a bar code reader, a remote management unit, and 2U rack-mounted hardware. DVD Rewritable/RecordableIf you need to perform backup on a budget, you can use a rewritable DVD drive. Usually, dual-layer (DL) rewritable DVD drives can be substituted for DVD-ROM or rewritable CD drives when a server is first configured, or they can be added later. The native capacity of single-layer DVD media is 4.7GB. If you use DL media, each disc can hold 8.5GB. DVD rewritable media is a good choice for backups of work-in-progress because the media can be erased and rewritten later. Conversely, DVD recordable provides durable archival storage. Most server backup programs designed for small and medium businesses support DVD rewritable/recordable drives. Note that the NT Backup utility that is built in to Windows 2000 Server and Windows Server 2003 cannot span a backup to multiple rewritable DVDs or CDs unless Firestreamer-RM is installed.
Limitations of Tape AlternativesTape alternatives have some limitations compared to tape backups, including the following:
Tip The Firestreamer-RM program adds support for rewritable DVD media, Iomega REV, and other types of removable-media drives to the NT Backup program used by Windows 2000 Server and Windows Server 2003 (including x64 and IA-64 versions); it also works with Windows XP. Firestreamer-RM supports volume shadow copy (enabling backups of open files), compression and data encryption, media and drive spanning, remote media via iSCSI, Microsoft Automated System Recovery, and other features. For more information and a free trial, go to the Cristalink Limited website, at www.firestreamer.com/Default.asp. |