Continuous Data Protection

Executive Summary: Continuous Data Protection’s (CDP’s) real value is in a product’s ability to go beyond simply providing continuous backup--to also support larger objectives. Compare CA XOsoft WANSyncHA, SonicWALL CDP 3.0 on the SonicWALL CDP 4440i appliance, Microsoft System Center Data Protection Manager (DPM) 2007, and TimeSpring Software’s TimeData to determine which CDP product is right for your environment.

As I conducted my research to write this review, I learned that the term continuous data protection (CDP) has a variety of meanings. To some, CDP means an ability to back up changed data at regular intervals. Broader definitions include network and server protection. For the purpose of this article, I’m defining true CDP as the ability to recognize changes to data at an application’s transaction level, as well as the ability to recover the state of the data to the point in time represented by the completion of any transaction. Many organizations don’t need the point-in-time recovery enabled by true CDP products to meet their Recovery Point Objectives (RPOs) for an acceptable level of data loss resulting from an incident. An additional measure of a CDP application’s suitability to an organization includes its ability to meet Recovery Time Objectives (RTOs)—that is, how quickly the application can be back up and running after an incident. In the following reviews, I try to give you a sense of the process and level of effort each product requires during recovery, to help you determine whether the product fits your applications and requirements.

Although many products are marketed as CDP solutions, I was able to consider only a few for this review. I narrowed the field by looking for products that offer support for two of Microsoft’s key applications: SQL Server and Exchange Server. I focused my testing on SQL Server support. I didn’t consider applications that occurred to me as primarily backup solutions.

During testing, I found that CDP’s real value proposition is in a product’s ability to go beyond simply providing continuous backup—to also use CDP to support larger objectives. A common thread among the four products I ultimately reviewed is their ability to maintain copies of protected data both locally and at a remote location in support of disaster recovery scenarios. Beyond that, the four products have more differences than similarities. CA XOsoft WANSyncHA replicates data to a second, potentially remote, server with support for automatic failover, failback, and point-in-time data rewind for recovery from events that corrupt data. SonicWALL CDP 3.0 on the SonicWALL CDP 4440i appliance, as I only discovered in testing, doesn’t support true transaction-level CDP for SQL Server; instead, it captures SQL Server transaction logs as frequently as every 30 minutes and restores to the state represented by any log file. Like SonicWALL’s CDP solution, Microsoft’s System Center Data Protection Manager (DPM) 2007 offers near-CDP alternatives, providing full backup frequency as often as every 30 minutes—or, when the protected application supports differential or log backup, every 15 minutes. TimeSpring Software’s TimeData used with SQL Server captures transaction-level changes even for simple recovery model databases and can recreate database files representing the point in time you select, but it leaves you with the task of placing the data back into production.

CA XOsoft WANSyncHA
CA XOsoft WANSyncHA, see Web Figure 1, incorporates CDP technology into an application server high availability product. The CDP portion of WANSyncHA is intended to bridge the protection gap between snapshots. By relying on the existing known good application data states provided by traditional backup and snapshot technologies, WANSyncHA minimizes the disk space required for the transaction-oriented rewind data. As a high availability product, WANSyncHA maintains a usable replica of the protected application server and can quickly fail over to the replica when necessary. A key application feature called Assured Recovery simplifies periodic testing of the failover process, including a rollback of test transactions applied to the replica during testing. WANSyncHA works in 32-bit and 64-bit Windows environments, and with AIX, Linux, and Sun Solaris servers.

WANSyncHA has two installable components: the XOsoft engine, which runs on every server participating as a master or a replica; and the management console, WANSync Manager, which you can install on any Windows workstation or server. Installation requirements are pretty basic. In a SQL Server environment, both the master server and the replica server must have the same configuration—both must be running the same service pack and hotfix level, as well as have the same storage configuration for protected databases. The management console, if you plan to use the remote installation facility, must run Microsoft .NET Framework 2.0. The installation procedure is well documented in the Operations Guide for the application you plan to protect. Because I used SQL Server for testing, I used the WANSyncHA SQL Server Operations Guide. I installed WANSync Manager and the XOsoft Remote Installer on the Windows XP system I was using; basic installation was quick and painless. Installing the XOsoft engine on the master and replica SQL Server machines of my choice was similarly easy.

The XOsoft engine, running as a service on each participating server, is WANSyncHA’s interface to each supported application—Microsoft IIS, Exchange, SQL Server, Oracle, and NTFS, including 64-bit versions of supported applications. You can use the WANSync Manager to create WANSync scenarios that control what the engine does. The wizard-driven process is easy to complete. After I selected a SQL Server high availability scenario, the wizard had me select master and replica SQL Server machines—the servers I had previously installed the XOsoft engine on—and then displayed the SQL Server instances and databases it found on the master server. I selected check boxes to indicate the databases I wanted to protect. Next, the wizard displayed the directories holding the database files that WANSyncHA would replicate. A properties page provides options to tailor WANSyncHA’s behavior on the master and replica servers. By default, CDP—the data rewind capability—is turned off, so I enabled it and configured the maximum disk space utilization. The next screen displays default switchover properties, including the method WANSyncHA will use to redirect network traffic to the replica server. The default is to redirect the application’s DNS name to the replica’s IP address. You can configure switchover to occur automatically when WANSyncHA detects failure of the master, or manually. Similarly, you can configure replication back to the master after switchover to start automatically or manually. WANSyncHA caches updates locally when the destination server is unavailable, and sends the data when communication is restored. WANSyncHA will use the Assured Recovery feature to schedule integrity testing to run periodically, or let you trigger it manually. By default, Assured Recovery performs only basic testing (i.e., connecting to the database). You can script more complex testing to meet your needs. Near the end of the scenario creation wizard, WANSyncHA runs more than 100 proactive configuration checks to help prevent unexpected problems later. When complete, the wizard offers the option to run the scenario—performing initial replication and beginning data protection. I selected this option, and when initial replication completed, WANSyncHA produced an HTML report detailing the data sets that were replicated. Figure 1 shows the active scenario status, displayed by WANSync Manager.

To test WANSyncHA, I used an application that writes system events to a SQL Server database. I used the application’s status screen to note when it was successfully connected to the database. With automatic switchover configured, I performed several failover and manual switchover tests. In each case, it took both my application and WANSync less than a minute to notice the absence of the active server. WANSync Manager displayed the progress of the switchover as the XOsoft engine on the stand-by server started SQL Server services and altered the DNS name of the primary server to point to the stand-by server. Within a minute or two, my application again reported a successful connection to the database server, now operating on the alternate system. After bringing the original server back online I performed a manual switchback, and it worked much the same—only in reverse. This process could be lengthy in a production environment, because WANSync, not knowing the state of the database on the primary server, must fully replicate the database back to the primary server before the switchback can occur. When testing switchover with both servers staying online, however, you can instruct WANSync to perform reverse replication from the secondary-now-active server back to the primary-now-stand-by server, and avoid the need to fully replicate the database when you switch back.

Next, I tested the data rewind capability. Although the documentation implies that you can simply stop replication to a stand-by server, I had to stop the scenario by clicking the stop scenario icon, stopping database operations on both the active and the stand-by servers. A data rewind operation can use either server as the source, and either replicate the new version of the database to the other server, or leave the other server unchanged. WANSync Manager presented me with a list of available timestamped checkpoints from which to choose. I selected the option to leave one server unchanged, selected a checkpoint, and ran the rewind. I checked both servers and found that the record count of a key table was unchanged on one server and reduced on the other server, as I expected. I was able to perform incremental data rewind operations, checking the state of the altered database after each rewind operation, as you would need to do if you were uncertain which checkpoint file would result in the most current, clean data.

Summary
CA XOsoft WANSyncHA 4.0.72
PROS: Maintains a remote server replica and supports automatic failover; leverages snapshot and traditional backup data to minimize the transaction-oriented storage requirements; Assured Recovery simplifies periodic testing of recovery procedures; data rewind operations work quickly for point-in-time recovery
CONS: Switching back after a failover caused by loss of the primary server requires a full replication of data back to the original primary server
RATING: 4.5
PRICE: $2,000 to $7,200 per server, depending on the server’s OS (Virtual Machine, Standard, Enterprise, Cluster) and applications to be protected (files, SQL Server, Exchange)
RECOMMENDATION: CA XOsoft WANSyncHA combines data rewind with application failover to a remote server for both offsite data protection and rapid application recovery. When you need true CDP with rapid remote application recovery, look at WANSyncHA first.
CONTACT: CA • 800-225-5224 • www.ca.com/us

SonicWALL CDP 4440i
SonicWALL’s CDP appliances are based on technology SonicWALL obtained through its acquisition of Lasso Logic. These appliances provide real-time backup for permanently and intermittently connected Windows systems. The models differ in raw storage capacity. The low-end 1440i has one 160GB IDE disk, the 2440i, see Web Figure 2, a 250GB IDE disk, the 3440i two mirrored Serial ATA (SATA) disks (size unspecified), and the 4440i three SATA disks in a RAID 5 configuration. Product literature reports compressed capacities from 192GB to 1.2TB. I tested the SonicWALL CDP 4440i, the largest of SonicWALL’s four CDP appliance models; its Enterprise Manager reported about 550GB of storage capacity. All the models have a single enabled Ethernet connection. The 3440i and 4440i support Gigabit Ethernet and include a second, currently unusable network interface. The two higher-end appliances also employ an advanced compression algorithm to make more efficient use of available disk space.

All models support open file backup. For users, CDP supports protection of Microsoft Office Outlook (through version 2003) and Outlook Express. All but the 1440i support backup of Active Directory (AD), SQL Server, and Exchange. When I selected the SonicWALL CDP appliance for review, I was under the impression that it supported true CDP for SQL Server machines—that is, a transaction-oriented backup allowing any-point-in-time restore. In fact, CDP supports recovery to the level of an individual transaction log backup, which the SonicWALL CDP device lets administrators schedule as frequently as every 30 minutes.

SonicWALL offers several optional features and services. Site-to-Site Backup lets you replicate backup data to one or more remote CDPs. An Offsite Data Backup Service lets you store backup data sets remotely at SonicWALL-managed sites, using encrypted transmission and stored in an encrypted format. Bare Metal Recovery for servers and workstations lets you recover a full system to new hardware, with all models including one or more workstation recovery licenses, and the 3440i and 4440i bundled with one and two server licenses respectively. Ongoing support services and software (including firmware) updates also require optional contracts, costing $1,679 and $1,359 for one year, respectively.

A Getting Started Guide walked me through the initial installation and configuration. I was able to use the 4440i’s Web interface to configure the appliance for my network. I downloaded the current SonicWALL CDP software package and installed it on the XP system I wanted to use as the management console. The software package installed the CDP Agent, which is the key client-based component. The agent explores the local system for supported applications and monitors selected applications and directories (the ones you configure) for changes to data, sending new and changed data blocks to a CDP device. The software package also installed two user interfaces. The CDP Enterprise Manager is used to configure reporting, alarms, and data recovery, as well as policies for use with agent systems. The CDP Agent Tool provides users on protected systems (those with the agent installed and configured) with an interface they can use to configure and monitor local CDP operations and to recover file versions. The software installation procedure also installed a service and added three programs to the Windows Firewall Exceptions list. The Getting Started Guide indicated that I’d be presented with “Complete” and “Custom” options, but I wasn’t. Apparently, the Enterprise Manager is always installed along with the agent on protected systems. I used the Enterprise Manager to configure basic administrative settings, including the password that protects access to the 4440i’s configuration.

Enterprise Manager also lets you create agent policies in which you can specify a disk quota for the agent, default folders and applications to protect, and backup exclusions at the file extension level. The policy feature doesn’t seem to be fully developed; it presented only Outlook and Outlook Express as the application options and didn’t give me an option to configure SQL Server-related or Exchange-related policies. Nor did it allow browsing either local or remote root (e.g., C$) drive shares to assist the creation of file backup policies. Because policies are the only tool that allows remote management of CDP devices’ backup configuration, a more complete policy feature would be extremely useful. Instead, administrators must use the Agent Tool installed on a computer to configure protection for that system. Remote configuration is possible using a remote desktop application.

I used the Agent Tool to designate a directory on my XP console for protection. The agent immediately backed up the directory to the 4440i. As I altered files in that directory, I was able to display and restore previous versions of a file to any location, including the original. This method for creating secure file version backups for local users is both easy and effective. Note that CDP supports protection of local disks but not remote file shares.

Because I was testing recovery in a SQL Server environment, I installed the agent on a SQL Server 2005 system with several active databases. I found that the application-specific CDP documentation is surprisingly sketchy. Discussions of SQL Server backup and recovery in the CDP 3.0 Administrators Guide are only half a page, and one page, respectively—and they simply tell you the steps to follow. Information related to AD and Exchange backup and recovery is similarly brief, and I found no similar discussion related to Outlook or Outlook Express. I called SonicWALL support to fill in some of the gaps. I learned that the agent uses the standard SQL Server API to perform full, differential, and log backups, so CDP won’t create log backups for databases set to the simple recovery model.

The facilities for protecting and restoring SQL Server databases are easy to use, with few options. After installing the agent and tools to a SQL Server 2005 system, I was able to quickly configure protection for several databases. For each database I was able to specify the backup interval for full, differential, and log backups, which default to monthly, weekly, and every two hours, respectively. CDP retains two full backup files, as well as associated differential and log backups. Recovery of a SQL Server database is similarly simple. As Figure 2 shows, you select Restore Database from the Agent Tool on the protected server; click the full, differential, or log backup file that represents the point in time you want to restore to; and specify a temporary disk that CDP will use for staging the backup. CDP then performs the restore. A second Restore to Disk option is similar but simply copies the necessary .bak backup files to the directory you designate. You can restore these .bak files with standard SQL Server facilities, or maintain copies to meet requirements for long-term storage.

Summary
SonicWALL CDP 3.0 on the SonicWALL CDP 4440i Appliance
PROS: Easy to implement data protection appliance for SQL Server, Exchange, AD, and NTFS files; optional features support automatic offsite replication of protected data; CDP 3.0 makes recovery to a previous state simple, with automatic selection of the correct set of backup files
CONS: Rather than supporting true transaction-aware CDP for SQL Server, SonicWALL’s CDP 3.0 recovers to the state contained in a log backup, which you can configure the SonicWALL appliance to capture as frequently as every 30 minutes; incomplete support to configure protection for a system remotely—alternatives include local configuration or use of a remote desktop product
RATING: 3.5
PRICE: $7,999 to purchase; support contracts start at $1,679 for one year of 5 ´ 8 support with software updates
RECOMMENDATION: Take a look at SonicWALL’s CDP line if the 4440i’s storage capacity and the 30-minute recovery point meet your needs, and if you can live with local or remote desktop access to configure protected systems. The appliance is effective and easy to use, especially when paired with one of the optional offsite replication alternatives.
CONTACT: SonicWALL • 888-557-6642 • www.sonicwall.com/us

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