Disk-to-Disk-to-Tape Backup
Fortunately, there are new methods of backup to turn to. One solution that's been around a few years is disk-to-disk-to-tape backup. At its simplest, disk-to-disk-to-tape means that backups are written to a disk array somewhere on the network, then the array's contents are later written to tape. Disk-to-disk-to-tape solutions often offer advanced capabilities that you just can't achieve through traditional backups.
For instance, disk-to-disk-to-tape backup solutions offer continuous data protection (CDP). Snapshot backups are taken on a periodic basis throughout the day; the frequency of snapshots varies by product. Each snapshot typically contains only the data that has changed since the previous snapshot was created. This type of backup eliminates the need for a large backup window. Because backups are made throughout the day, there's no colossal backup late at night, although the systems does need to copy the disk-based backup to tape. Also, because small backups are taken on a nearly continuous basis, the impact on the server’s performance is often far less than during a traditional backup.
Storing tapes offsite can result in longer downtime because you need to retrieve the tapes before a recovery operation can begin. With a disk-to-disk-to-tape solution, you won't have this problem except in the most extreme circumstances. The disk-based backups are readily available, and you can initiate a recovery operation without waiting to retrieve a tape from offsite storage. Tapes are still stored offsite, but the tapes act only as a contingency against the destruction of the facility or against the loss of the storage array that contains the backups.
As I mentioned, tape capacity can be a problem with traditional backups because the Store tends to grow exponentially and tape capacity remains static. Unfortunately, you can never completely get away from this problem because even disk-based backups are eventually written to tape as an extra safeguard. However, the size of the backups when they're written to disk isn't as big a problem because in most cases you can add additional disks to the storage pool on the backup server as necessary.
Data Protection Manager
There are many different disk-to-disk-to-tape backup solutions on the market, such as Lucid8's DigiVault, CA XOsoft CDP Solo (formerly Enterprise Rewinder), and FalconStor Continuous Data Protector. Microsoft offers its own product, System Center Data Protection Manager, which is specifically designed for backing up Exchange Server. Of course, you can use DPM to backup your other servers as well.
DPM is a CDP solution. Rather than backing up your Exchange organization once a day, DPM performs backups continuously. In fact, you can configure DPM to make backups as frequently as every 15 minutes. Keep in mind that it doesn't back up the entire Store every 15 minutes, which would be impossible for just about any real-world Exchange installation. Instead, DPM backs up only the transaction logs during these frequent backups.
The Store itself is backed up once a day with an express full backup, which uses Microsoft Volume Shadow Copy Service (VSS) to take a snapshot of the database, then write that snapshot to the backup storage array. Assuming your server has adequate disk space, you can retain as many as 512 express full backups—meaning that you can have that many backup points to choose from when you need to restore. So you can perform a point-in-time restore of the Exchange database and restore the server to the point just before a problem started.
It takes much less time to create backups with this method than it does with traditional tape backup. After all, transaction logs are backed up throughout the day, so there's a lot less work to be done when the express full backup runs. They still require some system resources, but those resources are released much more quickly than they would be if you were running a traditional backup. Furthermore, express full backups only back up the portions of the database that have changed since the previous backup. So you get faster backups and much less disk space consumption than if you were backing up the entire database every time.
VSS-Based Backups
Most, if not all, CDP solutions for Exchange rely on VSS. VSS is the mechanism that allows snapshots of data to be made, regardless of whether a file is open. If you're using a CDP solution or a traditional backup that incorporates VSS, you need to be aware of some limitations. For starters, you can't make a VSS backup of an individual database. You must backup storage groups as a whole because all of the databases within a storage group share a common set of transaction logs. You also can't simultaneously back up multiple storage groups on an Exchange server.
When you run a VSS backup of Exchange, the backup software must ensure that no changes are made to the database or to the transaction logs during the backup, but it must also keep these items available to users. To accomplish this, the databases and transaction logs are temporarily locked; any messages sent or received while the database is locked are placed in a queue. The backup software quickly makes a read-only copy—a snapshot—of the database, then releases the lock.
Snapshot data isn’t streamed to tape—at least not until later; it's written to a disk volume first. To make this process practical, the volume must be large enough to accommodate the snapshots and fast enough that the snapshots can be made before the database lock becomes disruptive to end users. Therefore, Microsoft recommends using a SAN for snapshot backups.
Continuous Replication Solutions
With Exchange 2007, Microsoft introduced the concept of continuous replication in the form of local continuous replication (LCR) and cluster continuous replication (CCR); Exchange 2007 SP1 introduced standby continuous replication (SCR). Although they're not complete backup solutions in themselves, these replication methods do provide you with a way of making your backups more efficient.
The continuous replication features in Exchange 2007 use a technique called log shipping to make backup copies of the transaction logs in an alternate location. When you use LCR, the logs are written to a separate volume on the same physical server. CCR works similarly, but the log files are written to a separate server. SCR replicates data to a remote site. The end result with each method is a backup copy of the database and its log files that you can use to restore data in the event of a failure.
Obviously, the point of using continuous replication is to provide yourself with an extra safeguard for your data, but this type of protection alone isn't enough because you're not generating a removable backup. But continuous replication technology can be used to help make your backups more efficient. When you use continuous replication, you can run a traditional tape-based backup against the replicated database rather than the production database and thereby suffer much less of a performance impact during the backup process.
DPM is designed to work with continuous replication. If you use CCR or SCR, DPM lets you perform your backup on the copy of the Exchange database, which helps prevent load from being placed on your live mailbox server.
Go Modern
In today's economic climate, companies can't afford to rely on outdated systems when there are quicker and more reliable alternatives. If your organization still relies exclusively on traditional tape-based backups, it's time to investigate a more modern approach. Disk-to-disk-to-tape and CDP solutions can help you overcome some of the problems associated with traditional backups.