Backing Up to Disk Going Mainstream
By Tony Asaro
Senior Analyst, Enterprise Storage Group

D2D or not D2D? Actually, that is not the question. Backing up to disk is one of those things that just makes sense. The price of hard drives is decreasing; data growth is off the charts; backup windows are shrinking; reliable recovery of data is becoming requisite; and Disk-to-Disk (D2D) technology is advancing.

The Enterprise Storage Group (ESG) recently completed a report, The Evolution of Enterprise Data Protection, which surveyed over 220 IT managers. Based on this ESG research the majority of these users are using or will be deploying D2D solutions of some variation. The benefits are clear:

• Increased backup performance
• Decreased time to recover
• Ensured data integrity and recoverability
• Media management issues

The issue is not whether to implement a D2D solution but what options are available and which will solve the problems to meet your needs.

Backup to Disk (B2D)
On the surface, backup to disk is very straightforward. Most major backup software applications allow users to backup to a disk target. Customers did not back up to disk in the past due to the high cost of disk storage space. Today low cost, high capacity ATA drives makes backing up to disk economically practical.

But backing up to disk is not as simple as it would seem. There are issues that IT managers should be aware of:

• The file systems on the media server qualified by the backup vendors typically have a 2 TB limitation. This will impact scalability, management and performance. You can get around this by installing a third-party file system but this will add cost and complexity.
• Using a host-based file system may expose you to viruses, file corruption, and accidental or malicious file deletion.
• The storage array used for the backup must be configured and managed and comes with all of the same technical challenges as any other SAN-attached system. Imagine managing 50 TB of backup data. Based on the 2 TB file system described above this would be mean that the storage administrator would have to support 25 file systems. And if you configure a LUN per file system, that equates to the management of 25 LUNs.
• Backup polices will more than likely need to be reconfigured to backup to disk.

Having said all of this, there are a number of customers that are doing exactly what is described above. In the ESG, the Evolution of Enterprise Data Protection report a large number of customers are using ATA drives in their storage arrays and are performing backup to disk. For them this solution is good enough for their purposes. But as the demand and storage capacity grows, IT managers may want to look at specially built D2D solutions, including backup to disk (B2D) appliances and Virtual Tape Libraries (VTL).

NetApp and Data Domain are two vendors that provide B2D products that resolve some of the issues described above:

• NetApp supports up to 8 TB in a file system; Data Domain supports 1.5 TB but they provide powerful compression capabilities that allow customers to effectively store more data with less actual used storage capacity. Data Domain claims that they can easily achieve 20x compression.
• Both NetApp and Data Domain have developed products that have their own file system. This eliminates the issue of file corruptions, viruses and file deletions. Data Domain claims that their file system was designed to recover from major disasters allowing users to rebuild data with just the meta-data.
• Both products are essentially NAS systems, which are usually easier to install and manage than a SAN storage array.
• Backup polices will still need to be modified to work with these solutions. We have spoken to customers that have done this and the changes are minimal.

Virtual Tape
Virtual Tape is not a new concept and has been widely used in IBM Mainframe environments for years. Approximately 60% of all IBM Mainframe data is protected by virtual tape. Virtual Tape solutions now support other operating systems including Windows, UNIX and Linux.

Virtual Tape Library (VTL) solutions are storage subsystems that emulate a tape library and use RAID protected hard drives to store the data. Typically the VTL solution has its own file system, emulates multiple tape libraries, and provides additional performance boosts through load balancing and large block sizes.

The advantages of Virtual Tape solutions are:

• VTL solutions support their own file system that provides larger storage capacity and reliability. The amount of capacity ranges depending on the product. Products from ADIC, Quantum and Sepaton support up to 40, 64 and 200 TB respectively.
• These systems are completely transparent since they emulate the tape library and therefore policies do not need to be re-written. Customers that have deployed VTL solutions are using them in their production environments out of the box in a few short hours.
• VTL solutions should provide a significant improvement in backup performance since these solutions typically provide load balancing and support large block sizes.
• Restore from VTL should be much faster than tape.
• As mentioned above, since VTL solutions have their own file system the reliability and recoverability should be rock solid.

There are a handful of VTL providers with a mixture of startups and established companies providing products in this space (see table 1):
 

Conclusion
ESG research has found that over 50% of customers that we surveyed believe that all of their data will be backed up to disk at some point in its lifecycle. Additionally, nearly half of the customers surveyed are already backing up to disk. Customers will see more solutions being offered in 2004 by new and established vendors, which will help with the adoption rate of D2D solutions. Customers that have not deployed a D2D solution are primarily concerned with cost of the products and are dealing with other higher priorities. Early adopters have deployed D2D to improve backup performance; rapidly restore data; ensure data integrity and recoverability; and manage their people resources more efficiently. The IT community has started to embrace D2D and its use will become a more strategic and requisite part of an overall data protection strategy.

Tony Asaro is a senior analyst for the Enterprise Storage Group responsible for the management of the ESG Lab service. Tony has extensive experience and expertise on storage subsystems, NAS solutions, data management software and SAN infrastructure. Tony works with both storage vendors and end user customers evaluating storage solutions, assisting with strategic directions and pricing strategies. Tony has worked in the high-tech industry for over 17 years as a systems engineer, product manager and project manager. You can contact Tony at tony@esglab.com.


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