Tài liệu Disaster Recovery: Backing Up and Restoring docx

Disaster Recovery: Backing Up and Restoring E very MIS or network administrator has a horror story to tell about backing up and restoring systems or data. One organization, where we now manage more than a dozen backup servers, has data processing centers spread all over the United States, and all are inter-connected via a large pri- vate wide area network. In mid-1999, a valuable remote Microsoft SQL Server machine just dropped dead. The IT doctor said it had died of exhaustion . . . five years of faithful service and never a day’s vacation. After trying everything to revive it, we instructed the data center’s staff to ship the server back to HQ for repairs. The first thing we asked the IT people at the remote office was: “You’ve been doing your backups everyday right?” “Sure thing,” they replied. “Every day for the past five years.” They sounded so proud, we were overjoyed. “Good, we will have to rebuild your server from those tapes, so send them all to us with the server.” To cut a frustrating story short: The five years’ worth of tapes had nada on them, not a bit nor a byte. Zilch. We spent two weeks trying to make sense of what was on that SQL Server computer and to rebuild it. We refuse to even guess the cost of that loss. We have another horror story we will later relate, but this example should make it clear to you that backup administra- tion, a function of disaster recovery, is one of the most impor- tant IT functions you will have the fortune to be charged with. Backup administrators need to be trained, responsible, and cool people. They need to be constantly revising and refining their practice and strategy; their companies depend on them. 17 17 CHAPTER ✦✦✦✦ In This Chapter Understanding Backup Practice and Procedure Removable Storage and Media Pools Using the Backup Tools that Come with Windows 2000 ✦✦✦✦ 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 643 644 Part V ✦ Availability Management This chapter serves as an introduction to disaster recovery/backup-restore proce- dures on Windows 2000 networks, the Backup-Restore utility that ships with the Windows 2000 operating system, and the Windows 2000 Removable Storage Manager. Before we get into this chapter, we should consider several angles on the backup/ restore functions expected of administrators. Why Back Up Data? You back up for two reasons, and even Windows 2000, with its fancy tools, rarely highlights the differences: ✦ Record-keeping (such as annual backups performed every month) ✦ Disaster Recovery (DR) or System Recovery You should make an effort to decide when a file is no longer valuable to the disaster recovery period, and then it should be archived out for record-keeping. Depending on your company’s needs, this may vary from a week to a couple of weeks, or from a month to a couple of months, and even years. There is no point buying media for annual backups for a site you know is due to close in six months. What To Back Up Often, administrators back up every file on a machine or network and dump the whole pile into a single backup strategy. Instead, they should be splitting up our files into two distinct groups: System and Data. ✦ System files comprise files that do not change between versions of the applica- tions and operating systems. ✦ Data files comprise all the files that change every day, such as word-processing files, database files, spreadsheets files, media files, graphics files, and configura- tion files (like the registry, DHCP, WINS, DNS, and the Active Directory data- bases). Depending on your business, data files can change from 2 percent a day on the low side to 80 percent a day on the high side. The average in many of the businesses for which we have consulted is around 20 percent of the files chang- ing every day. And, you must also consider the new files that arrive. Understanding the requirements will make your life in the admin seat easier, because this is one of the most critical of all IT or network admin jobs. One per- son’s slip-up can cause millions of dollars in data loss. How often have you backed up an entire system that was lost for some reason, only to find that to restore it, you had to reinstall from scratch? “So why was I backing up the system,” you might 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 644 645 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring have asked yourself. And how often have your restored a file for a user who then complained he or she lost five days’ worth of work on the file because the restore was so outdated. It’s happened to us on many occasions and is very disheartening if you are trying so hard to keep your people productive. There is nothing worse than trying to recover lost data, knowing that all on Mahogany Row are sitting idle, with the IT director standing behind you in the server room, and discovering you cannot recover. The thought of your employment record being pulled should make you realize how important it is to pay attention to this function. We will delve into these two subjects in more depth in this chapter and explore how Windows 2000 helps us better manage our recovery and record-keeping processes. We will start by focusing on the data side of the backup equation and finally lead this discussion into system backup/restore. Understanding Backup Before you can get started using Windows 2000 Backup, or any other backup pro- gram, you need to know how backing up works and have a basic backup strategy in mind. Archive Bits The archive bit is a flag, or a unit of data, indicating that the file has been modified. When we refer to the setting of the archive bit, we mean that we have turned it on, or we have set it to “1.” Turning it off means we set it to zero or “0.” If the archive bit is turned on since we last backed up the file, it means that the file has been mod- ified since it was last backed up. Trusting the state of the archive bit, however, is not an exact science by any means, because it is not unusual for other applications (and developers) and processes to mess with the archive bit. This is the reason we recommend that a full backup be performed on all data at least once a week. What Is a Backup? A backup is an exact copy of a file (including documentation) that is stored on a storage media (usually in a compressed state) and kept in a safe place (usually at a remote location) for use in the event the working copy is destroyed. Notice that we placed emphasis on “including documentation,” because with every media holding backups, you need to maintain a history or documentation of the files on the media. This is usually in the form of labels and identification data on the media itself, on 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 645 646 Part V ✦ Availability Management the outside casing, and in spreadsheets, hard catalogs, or data ledgers in some form or another. Without history data, restore media will be unable to locate your files and the backup will be useless. This is why it is possible to prepare a tape for overwriting by merely formatting the label so that the magnetic head thinks the media is blank. There are various types of backups, depending on what you back up and how often you back it up: ✦ Archived backup: A backup that documents (in header files, labels, and backup records) the state of the archive bit at the time of copy. The state (on- off) of the bit indicates to the backup software that the file has been changed since the last backup. When Windows 2000 Backup does an archived backup, it sets the archive bit accordingly. ✦ Copy backup: An ad-hoc “raw” copy that ignores the archive bit state. It also does not set the archive bit after the copy. A copy backup is useful for quick copies between DR processes and rotations, or to pull an “annual” during the monthly rotation (we discuss this later). ✦ Daily backup: This does not form part of any rotation scheme (in our book anyway). It is just a backup of files that have been changed on the day of the backup. We question the usefulness of the daily backup in Backup, because mission-critical DR practice dictates the deployment of a manual or auto- mated rotation scheme (described later). Also, Backup does not offer a sum- mary or history of the files that have changed during the day. If you were responsible for backing up a couple of million files a day . . . well, this just would not fly. ✦ Normal backup: A complete backup of all files (that can be backed up), period. The term “normal” is more a Windows 2000 term because this backup is more commonly called a “full” backup in DR circles. The full backup copies all files and then sets the archive bit to indicate (to Backup) that the files have been backed up. You would do a full backup at the start of any backup scheme. You would also have to do a full backup after making changes to any scheme. A full backup, and documentation or history drawn from it, is the only means of per- forming later incremental backups. Otherwise, the system would not know what has or has not changed since the last backup. ✦ Incremental backup: A backup of all files that have changed since the last full or incremental backup. The backup software sets the archive bit, which thereby denotes that the files have been backed up. Under a rotation scheme, a full restore would require you to have all the incremental media used in the media pool, all the way back to the first media, which contains the full backup. You would then have the media containing all the files that have changed (and versions thereof) at the time of the last backup. 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 646 647 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring ✦ Differential backup: This works exactly as the incremental, except that it does not do anything to the archive bit. In other words, it does not mark the files as having been backed up. When the system comes around to do a differ- ential backup, it will rely on comparison of the files to be backed up with the original catalog. Differential backups are best done on a weekly basis, along with a full or normal backup, so as to keep differentials comparing against recently backed up files. What Is a Restore? A restore is the procedure you perform to replace a working copy of a file or collec- tion of files to a computer’s hard disks in the event they are lost or destroyed. You will often perform a restore for no reason other than to return files to a former state (such as when a file gets mangled, truncated, corrupted, or infected with a virus). Restore management is crucial in the DR process. If you lose a hard disk or the entire machine (for example, it is trashed, stolen, lost, or fried in a fire), you will need to rebuild the machine and have it running in almost the same state (if not exactly) as its predecessor was in at the time of the loss. How you manage your DR process will determine how much downtime you experience or the missing genera- tion of information between the last backup and the disaster — a period we call void recovery time. Understanding How Backup Works A collection of media, such as tapes or disks, is known as a backup set (this is differ- ent from a media pool, which we will discuss in a bit). The backup set is the backup media containing all the files that were backed up during the backup operation. Backup uses the name and date of the backup set as the default set name. Backup allows you to either append to a backup set in future operations or replace or over- write the files in the media set. It allows you to name your backup set according to your scheme or regimen. Backup also completes a summary or histories catalog of the backed-up files, which is called a backup set catalog. If your backup set contains several media, then the catalog is stored on the last medium in the set, at the end of the file backup. The backup catalog is loaded when you begin a restore operation. You will be able to select the files and folders you need to restore from the backup catalog. Removable Storage and Media Pools Removable Storage (RS) is a new service in Windows 2000 that takes away a lot of the complexity of managing backup systems. This service also brings network sup- port to Windows for a wider range of backup and storage devices. 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 647 648 Part V ✦ Availability Management Microsoft took the responsibility of setting up backup devices and management of media away from the old Backup application and created a central authority for such tasks. This central authority is known as Removable Storage and is one of the largest and most sophisticated additions to the operating system, worth the price of the OS license alone, and a welcome member on any network. If you are not ready to convert to a Windows 2000 network, you might consider raising a Windows 2000 “Backup” server just to obtain the services of Removable Storage. But Removable Storage is like an iceberg. In this chapter and in other parts of the book, we can only show you the tip. Exposing the rest of this monster service, and everything you can do with it, is beyond the scope of this treatise, and a full treat- ment of the subject would run into several chapters. To fully appreciate this service, and if you need to get into some serious disaster recovery strategies, possibly even custom backup and media handling algorithms, you should refer to the Microsoft documentation covering both the Removable Storage Service and its API and the Tape/Disk API. A good starting place is the Windows 2000 Server Operations Guide, which is part of the Resource Kit, discussed in Appendix B. We will, however, pro- vide you with an introduction to the service, coming up next. The Removable Storage Service Removable Storage comprises several components. But the central nervous system of this technology is the Removable Storage Service and the Win32 Tape/Disk API. These two components, respectively, expose two application programming inter- faces (APIs) that any third party can access to obtain removable storage functional- ity and gain access to removable storage media and devices. The Backup program that ships with the OS makes use of both APIs to provide a usable, but not too sophisticated, backup service. By using the two services, applications do not need to concern themselves with the specifics of media management, such as identifying cartridges, changing them in backup devices, cataloging, numbering, and so on. This is all left to the Removable Storage Service. All the application requires is access to a media pool created and managed by Removable Storage. The backup application’s responsibility is identify- ing what needs to be backed up or restored, and the source and destination of data; Removable Storage’s responsibility deals with where to store it, what to store it on, and how to retrieve it. Essentially, the marriage of backup-restore applications and Removable Storage has been consummated along client/server principles. The Removable Storage Service can be accessed directly by programming against the API. You can also work with it interactively (albeit not as completely as programming against the API) in the Removable Storage node found in the Computer Management snap-in ( compmgmt.msc ). The Removable Storage node is also present in the Remote Storage snap-in discussed in Chapter 21. Before we begin with any hard-core backup practice, let’s look at Removable Storage and how it relates to backup and disaster recovery. Removable Storage is also briefly discussed in Chapter 16. 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 648 649 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring Figure 17-1: The Removable Storage Snap-in The service provides the following functionality to backup applications, also known as backup or data moving and fetching clients: ✦ Management of hardware, such as drive operations, drive health and status, and drive head cleaning ✦ Mounting and dismounting of cartridges and disks (media) ✦ Media inventory ✦ Library inventory ✦ Access to media and their properties Access to the actual hardware is hidden from client applications. But the central component exposed to all clients is the media pool. To better understand the media pool concept in Removable Storage, let’s first discuss media. Backup media ranges from traditional tape cartridges (discussed at the end of this chapter) to magnetic disk, optical disk CD-ROM, DVD, and so on. More types of media are becoming available, such as “sticks” and “cards” that you can pop into cameras and pocket-sized PCs, but these are not traditional backup media formats, nor can they hold the amount of data you would wish to store. DVD, a digital video standard, however, is a good choice for backing up data because so much can be stored on a single DVD disk. Like the dynamic disk management technology discussed in Chapter 16, Removable Storage hides the physical media from the clients. Instead, media is presented as a logical unit, which is assigned a logical identifier or ID. When a client needs to store or retrieve data from media, it does not deal with the physical media, but rather with that media’s logical ID. The logical ID can thus encapsulate any physical media, the format of which is of no concern to the client application. 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 649 650 Part V ✦ Availability Management Although the client need not be concerned about the actual media, you, the backup administrator, have the power, by configuring media pools, to dictate onto which format or media type your backups should be placed. If this is confusing to you, it will become clearer when you understand media pools, discussed shortly. The benefit of the logical ID is patent, but a good example of its application is that the service is able to move data, represented by its logical ID, from one physical medium to another. This would be desirable if media is approaching the end of its life and the data needs to be moved to new cartridges. Media formats can be extremely complex. Some media allow you to write and read to both sides; others only allow access to one side. How media is written to and read from differs from format to format. Removable Storage handles all those pecu- liarities for you. Just like the Print Spooler service, which can expose the various features of thousands of different print devices, so can Removable Storage identify many storage devices and expose their capabilities to you and the application. (The pros and cons of each of the popular backup media formats are discussed at the end of this chapter). Finally, and most important from the cost/benefit aspect, Removable Storage allows media to be shared by various applications. This ensures maximum use of your media asset. The Removable Storage Database Removable Storage stores all the information it needs about the hardware, media pools, work lists, and more in its own database. This database is not accessible to clients and is not a catalog of which files have been backed up and when. Everything that Removable Storage is asked to do, or does, is automatically saved in this database. Physical Locations Removable Storage also completely handles the burden of managing media location, a chore once shared between the client applications and the administrator. But the physical location service deals with more than knowing in which cupboard, shoe- box, vault, or offsite dungeon you prefer your media stored in; it is also responsible for the physical attributes of the hardware devices used for backing up and restoring data. It is worthwhile to understand this section, because you will need such knowl- edge to perform high-end backup services that protect a company’s data. Removable storage splits the location services into two tiers: libraries and offline locations. If a media is online, then it is inside a tape device of some kind that can at any time be fired up to allow data to be accessed or backed up. If media is offline, then it means that you have taken it out of its drive or slot and sent it somewhere. Note 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 650 651 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring As soon as you remove media from a device, Removable Storage makes a note in its database that the media is offline. Libraries can be single tape drives or highly sophisticated and very expensive robotic storage silos comprising hundreds of drive bays. A CD-R/W tower, with 12 drives, is also an example of a library. Media in these devices or so-called libraries are always considered online, and are marked as such in the database. Removable Storage also understands the physical components that make up these devices. Library components comprise the following: ✦ Drives: All backup devices are equipped with drives. The drive machinery consists of the recording heads, drums, motors, and other electronics. To qualify as a library, a device requires at least one drive. ✦ Slots: Slots are pigeonholes, pits, or holding pens in which online media is placed, in an online state. When media is needed for a backup, a restore, or a read, the cartridge or disk is pulled out of the slot and inserted into the drive. When the media is no longer needed, the cartridge is removed from the drive and returned to its slot. The average tape drive does not come equipped with a slot, but all high-end, multi-drive robotic systems do. The basic slot-equipped machine typically comes equipped with two drives and 15 slots. Slots are typi- cally grouped into collections called magazines. Each magazine holds about five cartridges, and one magazine maintains a cleaning cartridge in one of the slots. You typically have access to magazines so that you can populate them with the cartridges you fetched from offline locations. ✦ Transports: These are the robotic machines in high-end libraries that move cartridges and disks from slots to drives and back again. ✦ Bar Code Readers: Bar coding is discussed later in this chapter. It is a means by which the cartridges can be identified in their slots. You do not require a bar code reader-equipped system to use a multi-drive or multi-slot system because media identifiers can also be written to the media. But bar code read- ing allows for much faster access to the cartridges, because the system does not need to read information off the actual media, which requires every car- tridge to be pulled from a slot and inserted into a drive, a process that could take as long as five minutes for every cartridge. ✦ Doors: Doors differ from device to device and from library system to library system. In some cases, the door looks like the door to a safe, which is released by Removable Storage when you need to gain access to slots or magazines. Many systems have doors that only authorized users can access. Some doors are built so strong that you would need a blowtorch to open them. On many cheaper devices, especially single drive-no slot hardware, the door is a small lever that Removable Storage will release so that you can extract the cartridge. Other devices have no doors at all, but when Removable Storage sends an “open sesame” command to the “door,” the cartridge is ejected out of the drive bay. 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 651 652 Part V ✦ Availability Management ✦ Insert/Eject Ports: The IE ports are not supported on all devices. IE ports pro- vide a high degree of controlled access to the unit in a multi-slot library sys- tem. In other words, you insert media into the port, and the transport goes and finds a free slot for it. Another way to comprehend the IE port function is to compare it to a valet service. You hand your car keys to the valet, and he or she goes and finds a free parking space for you. If the hardware you attach supports any or all of these sophisticated features, Removable Storage will be able to “discover it” and use it appropriately. There are dozens, if not hundreds, of devices from which to choose for backing up and storing data. Removable Storage, as we discussed, can handle not only tradi- tional tape backup systems, but also CD silos, changers, and huge multi-disk read- ers. If you wish to check if Removable Storage supports a particular device, follow the steps to create a media pool discussed in the section “Performing a Backup” later in this chapter. Media Pools A new term in the Windows operating system is the media pool. If you are planning to do a lot of backing up or have been delegated the job of backup operator or administrator, you will have a lot to do with media pools in your future backup- restore career. A media pool in the general sense of the term is a collection of media organized as a logical unit. Conceptually speaking, the media pool contains media that belong to any defined storage or backup device, format, or technology assigned to your hard- ware, be it a server in the office or one located out on the WAN somewhere, 15,000 miles away. However, each media pool can only represent media of one type. You cannot have a media pool that combines DVD, DAT, and ZIP technology. But you can back up your data to multiple media pools of different types if the client application or function so requires it. It may be easier to think of the media pool in terms of the hardware devices that are available to your system (such as a CD-R/W or a DLT tape drive). You should strive not to work with media pools from dissimilar devices, especially when backing up zillions of files. For example, you should stay away from creating media pools that consist of Zip drives, DLT tape drives, and a CDR-R/W changer. It would make man- aging your media, such as offsite storage, boxing, and labeling, very difficult, much like wearing a sneaker on one foot and a hiking boot on the other and then justify- ing walking with both at the same time because they both represent “pools” of walking attire. Removable Storage separates media pools into two classes: system pools and appli- cation pools. The Removable Storage Service creates system pools when it is first installed. By default, the Removable Storage Service is enabled and starts up when 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 652 [...]... 671 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring To perform backup and restores from and to any machine on the network, you must be either the administrator (signed on as) or be a member of the domain’s Backup Operator’s group As a domain Backup Operator, you can also do backups and restores in another domain if there is a trust between the domains Remember, you cannot back up the system-state... that makes full use of Backup on every server and computer on the network while performing the backups from a single backup server, running any choice of backup software Source and Destination We refer to sources and destinations when talking about backing up on any system So, open Backup and click the Backup tab In the left pane — your backup source — click the + box to expand your Desktop, as illustrated... procedures No matter how regularly you back up the data on your network, you can only restore up to the point of your last complete backup Unless you are backing up every second 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 657 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring of the day, which is highly unlikely and impractical, you can never fully recover the latest data up to the point of meltdown (unless... NT, and if running backup from the command line does not solicit a response from the server, try NTbackup You still call the software using NTBackup, so your NT 4.0 backup scripts can be easily ported You can type in the command line parameters and switches at the command line or prompt, and the OS will load and run the backup routines (or you can just use the “Run” service) This is a complex and cryptic... our tapes or disks and call it Full, or First Backup or Normal # 1 — whatever designates a complete backup of the system and collection of files and folders The first backup of any system is always a full backup, and the reason is simple Backup, and you, need a catalog or history of all the files in the backup list so that you can access every file for a restore and so that Backup can perform incremental... Length of Backup You should also work out how long your backups take It may be prudent to start your backups at one minute to midnight, but if morning swings around and your backups are still churning away, you will have hardly performed a backup and the file may become locked or substantially changed when systems and people log in and seize control again If your backup devices are backing up multiple... GUI, and that there is no different or alternative Backup application at work under the hood You begin your command line statement with the words Ntbackup backup The first exercise at this point is to clone the job we had earlier set up in Backup, that of backing up the system-state But as we earlier promised, we are going to use this backup in conjunction with a remote backup server Open the command... e-mail files On the other hand, a Remote Access Server, one of a group of WINS servers, and volumes that have no changing data on them are ideal candidates for image burns 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 665 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring The Open Files Dilemma Open files have always been the backup administrator’s nightmare on Windows NT Server, and this is still very... backup according to the procedures 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 677 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring we earlier discussed You should have had enough practice by now And you are ready to go from a development or trial backup to a production rotation scheme As soon as you have made a full backup set, label the members as discussed and then perform a second full backup... to step through it and understand all the features 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 673 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring To edit the job schedule, you can click on the Schedule Jobs tab at any time and load the Schedule Jobs calendar You can then double-click on any day of the month to start the Backup Wizard, or you can click a previously defined Job and load the Scheduler . Disaster Recovery: Backing Up and Restoring E very MIS or network administrator has a horror story to tell about backing up and restoring systems. complete backup. Unless you are backing up every second 4667-8 ch17.f.qc 5/15/00 2:07 PM Page 656 657 Chapter 17 ✦ Disaster Recovery: Backing Up and Restoring