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De-duplication Guides
Enterprise-class disk array purchase considerations
Disk storage is gaining attention as a preferred backup target, providing high levels of performance and reliability that tape media is hard-pressed to deliver. Techniques like RAID-6/DP, disk-to-disk (D2D) snapshots, internal storage tiering, and replication have emerged as important backup tactics, leveraging disk to shorten backup windows, reduce recovery point objectives (RPO) and speed recovery time objectives (RTO). However, selecting the right disk array for your enterprise isn't easy. Now that you've reviewed the essential issues involved in any backup acquisition, this chapter focuses on the specific considerations of enterprise-class disk arrays. You'll also find a series of specifications to help make on-the-spot product comparisons between vendors, like 3PARdata Inc., EMC Corp., Hitachi Data Systems Inc. (HDS), IBM and others.
Match the cost of disk to the value of data. Enterprise data can vary dramatically in its value to the enterprise, so choose disk products that suit the importance of that data. For example, if you intend to store mission-critical database content on the disk array, select high-performance, high-reliability Fibre Channel (FC) hard drives for the array. For less critical documents or other corporate media, you may opt for SAS or high-volume SATA drives that are slower but less expensive, and generally less reliable. Many arrays can support a variety of drive types, allowing you to implement multiple storage tiers within the same disk array -- allowing data to be migrated between tiers and usually resulting in a significant cost savings for the storage organization. Consider how a disk array will impact backup processes. Most IT organizations are used to tape-based backups using conventional backup software, so the introduction of a general-purpose disk array often causes unexpected disruptions to the backup process, forcing backup administrators to use new tools and adjust procedures to achieve adequate data protection. For example, snapshot and replication tools are significantly different than conventional backup software. Understand that internal changes will be needed to support new disk array products. Note that virtual tape libraries (VTL) are disk arrays that are specifically designed to emulate tape libraries, easing the impact on backup processes. VTL systems are covered specifically in the next chapter. Consider the impact of rebuild times on the backup process. Failed disks are replaced and their contents are then automatically rebuilt from the corresponding mirror disk or RAID group. However, the rebuild process takes time, which impacts production use of the array along with any backups scheduled during the rebuild time. You may not be able to access the affected RAID group (or access it at significantly lower performance levels) until the failed disk bas been rebuilt. Understand how to respond to disk faults and know how that impacts the backup processes. Advanced features like "pre-emptive rebuilds" can monitor a disk for signs of impending failure and start the rebuild process before a disk actually fails -- minimizing the rebuild time. Look for data compression technologies to extend disk capacity. As data volumes increase at 60% or more per year, the cost of new disk capacity can be a significant expense. Compression techniques are emerging to fit more data on less disk space, lowering the cost of additional storage. Conventional compression basically works by removing redundant data from each file -- making the files smaller and using less space. Data deduplication, also called commonality factoring or intelligent compression, provides single-instance storage, so only one copy of a particular block or file is actually stored on the array. For example, rather than saving 10 copies of a 100 MB PowerPoint presentation in a backup process, only one copy of the presentation is committed to disk. Note that content-addressed storage (CAS) platforms typically employ data deduplication, but the technology is extending to other disk arrays. CAS products are covered in a later chapter. Consider the disaster recovery implications of disk backups. Arrays typically support hot swapping between disks, but the disk drives themselves are generally not easily transportable. That is, you wouldn't pop out a 600 GB SATA drive from an array in New York City and send it to a storage facility in Des Moines, Iowa. Consequently, disks are on-site assets and subject to fire, flood and other disasters. Disk arrays are often protected with supplemental tape backups -- dubbed disk-to-disk-to-tape or D2D2T -- or replicated remotely to a secondary array across a wide area network (WAN). Return to the beginning
Tutorial on purchasing virtual tape libraries
Some organizations using tape-based backup are hesitant to change the backup tools and processes needed to accommodate disk array storage -- often forestalling any changes until backup demands reach crisis levels. Virtual tape libraries (VTL) bridge that gap, providing the benefits of disk storage in a system that accurately emulates a tape library to existing backup software. Thus, IT organizations can embrace disk storage with little, if any, retooling or learning curve. But VTL selection demands careful consideration particularly when it comes to capacity and retention time. Now that you've reviewed the essential issues involved in any backup acquisition, this Guide outlines specific considerations for VTLs.
Weigh the need for disk storage against current processes. Before incurring the expense of a new virtual tape library platform, consider the current backup window, recovery point objective (RPO) and recovery time objective (RTO). If backup objectives are met with tape, the addition of a VTL may be difficult to justify -- the added performance of disk storage would have no business impact. Organizations that are already leveraging other disk storage technologies with snapshot or replication tools may also see little benefit from VTLs. However, VTLs may be a worthwhile technology to shorten backup windows, RPOs and RTOs, where tape is currently in use. For example, an organization experiencing backup windows that routinely run over into production time (e.g. running through a weekend into Monday morning) may see a significant benefit from a VTL. Consider the compatibility and interoperability of the VTL platform. Virtual tape library systems and backup software are not universally compatible. Be sure that any prospective VTL system will be compatible with your existing backup software, such as EMC NetWorker or IBM Tivoli Storage Manager (TSM). In many cases, the VTL will emulate a number of tape drives (e.g., LTO-2, LTO-3 or LTO-4), which the backup software can access directly, requiring only a relatively minor reconfiguration of the backup software. Consider VTL storage capacity versus backup needs. VTL storage capacity is not endless -- VTLs only implement a finite amount of disk space. When planning a virtual tape library, understand the space needed for each backup and then multiply that by the length of time those backups need to be retained. For example, if you're backing up 5 terabytes (TB) each week and need to retain the backups for at least four weeks, the VTL would need at least 20 TB of capacity. Many users opt for considerably more capacity to meet burgeoning storage needs. Long-term storage scalability is often an overlooked attribute of VTL platforms. Look for data compression technologies to extend disk capacity. As with ordinary disk arrays, compression techniques are emerging to fit more data on less disk space. In addition to conventional compression, which removes redundant data from each file, data deduplication provides "single instance" storage so that only one copy of a file or block is actually stored on the VTL. Experts note effective compression levels for data deduplication approaching 50-to-1. For a virtual tape library, this increases the number of backups that can be stored locally. [See the Data Deduplication Special Report for more details on the current state of this technology.] Consider long-term archival storage of backed up data. A virtual tape library cannot hold a backup set forever. Once a backup set "ages out," it must be offloaded from the VTL to make space for new backups. In many cases, it's not acceptable to simply delete the backup set. Instead, the backup is offloaded to archival storage on a SATA disk array or tape library. The tape system that was displaced by a VTL is often redeployed as an archival storage system to create a disk-to-disk-to-tape (D2D2T) architecture. Return to the beginning
Virtual tape library specifications
Virtual tape library (VTL) systems use disk storage to improve backup and restore processes, allowing many organizations to move from tape to disk backups without disrupting current practices. High-end virtual tape library systems can use more than 1,000 SATA drives, offering hundreds of terabytes of raw storage, while emulating dozens of tape drives and thousands of tape cartridges, so they appear exactly like a tape library to many different backup software products. The following product snapshots highlight the key specifications for a cross-section of VTL systems/appliances with a minimum of 1 TB of disk capacity and storage area nework (SAN) connectivity of at least 500 MB per hour. The products were selected based on input from industry analysts and SearchStorage.com editors. Specifications are current as of November 2007. These specifications are periodically updated, and vendors are welcome to submit their updates and new product specifications to sbigelow@techtarget.com. Go to the first product snapshot, or select the desired product below: Bus-Tech Inc.; Mainframe Data Library Return to the beginning Product Snapshot #1 Product: Bus-Tech Inc.; Mainframe Data Library Usable capacity: In excess of one petabyte Return to the beginning Product Snapshot #2 Product: COPAN Systems Inc.; The Revolution 220T VTL (1) Usable capacity: 20.25 TB to 324 TB (compressed capacity; depending on drives) Return to the beginning Product Snapshot #3 Product: Copan Systems Inc.; The Revolution 220TX VTL (1) Usable capacity: 101.25 TB to 324 TB Return to the beginning Product Snapshot #4 Product: EMC Corp.; Disk Library (DL) 210 (1) Usable capacity: 4 TB to 24 TB (72 compressed) Return to the beginning Product Snapshot #5 Product: EMC Corp.; DL4100 (1) Usable capacity: 11.5 TB to 170 TB Return to the beginning Product Snapshot #6 Product: EMC Corp.; DL4200 (1) Usable capacity: 11.5 TB to 170 TB Return to the beginning Product Snapshot #7 Product: EMC Corp.; DL4400 (1) Usable capacity: 23 TB to 370 TB Return to the beginning Product Snapshot #8 Product: FalconStor; VTL-350 (1) Usable capacity: More than 512 TB can be attached Return to the beginning Product Snapshot #9 Product: Virtual Tape Library (VTL) Storage Appliance (VTL-S6) (1) Usable capacity: 3.75 TB with RAID 5 Return to the beginning Product Snapshot #10 Product: Virtual Tape Library (VTL) Storage Appliance (VTL-S12) (1) Usable capacity: 7.5 TB with RAID 6 Return to the beginning Product Snapshot #11 Product: Virtual Tape Library (VTL) Storage Appliance (VTL-S24) (1) Usable capacity: 16.5 TB with RAID 6 Return to the beginning Product Snapshot #12 Product: Virtual Tape Library (VTL) Virtual Appliance for VMware Usable capacity: 2.8 TB Return to the beginning Product Snapshot #13 Product: HP; StorageWorks 1000i Virtual Library System (1) Usable capacity: 1.5 TB Return to the beginning Product Snapshot #14 Product: HP; StorageWorks D2D 110 Backup System (1) Usable capacity: 750 MB Return to the beginning Product Snapshot #15 Product: HP; StorageWorks D2D 120 Backup System (1) Usable capacity: 1.5 TB Return to the beginning Product Snapshot #16 Product: HP; StorageWorks 6000 Virtual Library System (1) Usable capacity: 2.5 TB to 70.3 TB Return to the beginning Product Snapshot #17 Product: HP; StorageWorks 9000 Virtual Library System (1) Usable capacity: 30 TB to 300 TB Return to the beginning Product Snapshot #18 Product: HP; StorageWorks 12000 Virtual Library System (1) Usable capacity: 3 TB to over 500 TB Return to the beginning Product Snapshot #19 Product: IBM; Virtualization Engine TS7700 (1) Usable capacity: Up to 6TB (18TB with 3:1 compression) Return to the beginning Product Snapshot #20 Product: Network Appliance Inc.; NearStore VTL 1400 Usable capacity: Uncompressed data -- 128TB; 2:1 compressible data -- 256 TB; 3:1 compressible data -- 384 TB Return to the beginning Product Snapshot #21 Product: Overland Storage Inc.; REO 4500 (1) Usable capacity: 2 TB to 10 TB (up to 38 TB using expansion arrays) Return to the beginning Product Snapshot #22 Product: Overland Storage Inc.; REO 9100 (1) Usable capacity: 2.5 TB to 15 TB (up to 44 TB using expansion arrays) Return to the beginning Product Snapshot #23 Product: Quantum Corp.; DXi3500 Disk Backup and Replication Appliance with Deduplication Technology (1) Usable capacity: 1.2 TB to 4.2 TB Return to the beginning Product Snapshot #24 Product: Quantum Corp.; DXi5500 Disk Backup and Replication Appliance with Deduplication Technology Usable capacity: 3.6 TB to 10.8 TB |