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What is disk staging and how is it implemented?

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Votes: 1
Posted: 02 Oct, 2007
Disk Staging (Disk-to-Disk-to-Tape)

The Challenge - To minimize the interruption of normal system activity while, at the same time, providing mechanisms to protect and reliably restore data lost when either the primary server system or a client system fails.

The Solution - BRU Server Disk Staging in concert with core BRU™ functionality reduces the perceived backup window at the client level, reduces the backup verification window at the server level, and provides the high speed recovery of files from disk, rather than tape.

BRU Server Disk Staging - The concept of disk staging is the writing of backup data to hard disk first rather than directly to tape, traditionally a slower technology. Then, at the system administrator's discretion, the data contained in the disk staging area is committed to tape in a background process.

BRU Server Disk Staging uses a centralized disk farm attached to the server system running BRU Server. The Disk Staging area can be configured as all, or part of an attached Xserve RAID subsystem, or on a simple external Firewire disk. Because disk access is asynchronous, BRU Server's Staging allows multiple client systems to send their backup data streams simultaneously to minimize the effect of backup window downtime. Performance is limited only by the network's bandwidth.

BRU Server Disk Staging can be implemented on any filesystem that is available to the physical server system - locally attached, Fibre-Channel SAN, or Network attached (depending on network bandwidth). BRU Server incurs very little overhead and can effectively be installed on the primary network server as shown in Figure 1 when the server is not task intensive. Backup data stream paths from client groups A, B and C can be directed to the Staging area.

Disk Staging Figure 1

When the primary server is task intensive, it is suggested BRU Server and its associate Disk Staging area be implemented as a separate backup system server attached on the network as shown in Figure 2. The separate BRU Server backup system can be implemented on a G4, G5, or an Xserve system. Whether or not the primary server is task intensive, implementing a separate backup system server is recommended because it removes the data protection function from the primary server's duties and provides the highest level of performance.

Disk Staging Figure 2

The benefits of implementing BRU Server Disk Staging include:

  • The perceived backup window at the client system level is virtually transparent following the first full backup of the client system because the subsequent backups will be executed in seconds, depending on the amount of changed data to be backed-up.
  • Files contained in the Staging area can be near-instantaneously recovered
  • Exceptionally fast data backup verification because BRU Server does not require access to system primary storage to fully verify backups. The verification of data contained in the staging area is executed at the throughput performance level of the subsystem, which can be significantly faster than data verification conducted on tape media.
  • Data written to the BRU Server Disk Stage can be fully verified in the same manner as verifying a tape archive to assure accuracy. Additionally, a single file can be retrieved from tape when the data has up-Staged from the BRU Disk Stage to the tape archive. Other backup tools write multiple file images to tape from their disk stages and require the complete image be restored from tape back to the disk stage prior to retrieving a target file.

A Caveat - The ultimate goal of backing up data is to protect it from irreplaceable loss. While writing to a disk farm staging area provides significant benefit to minimize the intrusion of a backup process, the ultimate commitment of data to tape provides the long-term assurance of data availability and recoverability. A good tape backup strategy that includes off-site tape storage in concert with disk staging delivers the highest backup system performance, reliability and data availability.

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