Compaq ProLiant 1000 Compaq Backup and Recovery for Microsoft SQL Server 6.X - Page 15

Compaq Backup and Recovery for Microsoft SQL Server 6.x Page 15 In this chapter, we will analyze some key benefits and limitations of various backup and recovery products, and provide some considerations to help you choose the hardware and software best suited for your environment. In this paper we have chosen to evaluate the Compaq DLT (Digital Linear Technology) family of tape drives, which includes the 10/20-GB DLT, 15/30-GB DLT, and 35/70-GB DLT tape drives. Other, older tape technologies such as the QIC (Quarter Inch Cartridge) and DAT (Digital Audio Tape) drives are also supported by Compaq but are not discussed here.13 The Compaq Digital Linear Tape (DLT) drives were designed to meet the growing backup needs of large computing environments, providing greater performance, capacity, and reliability from a PC server tape solution than ever before. The DLT ensures data integrity through multiple checks including: error-correction-code (ECC) on every 64KB of tape data, cyclical-redundancy-check (CRC) on each 4KB of tape data, end-to-end CRC on each record overlapped with parity from the SCSI bus, and internal parity checking on the 2 MB memory buffer14. DLT drives record and read data using multiple, parallel tracks in a serpentine (alternating end-to-end) fashion. The DLT tape media supports a 128-track format, and DLT cartridges are specified to last 500,000 passes over the read/write head which equates to 7,812 backups using the entire tape capacity. The head life of the drive itself is estimated at 30,000 hours under continuous operation. All Compaq DLT drives provide built-in hardware data compression using the DLZ (Digital LempelZiv) algorithm. The 10/20-GB DLT drive (DLT2000) supports 3 density formats, the most efficient of which yields 10GB of storage space uncompressed and 20GB with 2:1 compression. The 15/30-GB DLT drive (DLT2000XT) supports 4 density formats, the most efficient of which yields 15GB of storage space uncompressed and 30GB with 2:1 compression. The 15/30 supports a superset of the 10/20 formats, so that it can read any tape recorded on a 10/20; but the 10/20 cannot read a tape that was recorded on the 15/30 using the highest (15GB) format. The 35/70-GB DLT drive (DLT7000) supports a superset of the other drives' formats, and offers a native format providing 35GB of capacity, or 70GB with 2:1 compression. The 10/20-GB and 15/30-GB DLT drives do not differ in performance, and are both capable of 4.5GB/hr (1.25MB/sec) throughput with data compression disabled (up to 9.0 GB/hr with 2:1 compression). The 35/70-GB DLT drive however, offers not only enhanced capacity but also enhanced performance, being capable of up to 18.0 GB/hr (5.0 MB/sec) throughput with data compression disabled (36.0 GB/hr with 2:1 compression). These high-performance, high-capacity and high-dutycycle backups make the DLT ideal for storage of large, mission critical databases like those found in many SQL Server environments. Table 1 summarizes the tape cartridge support of tape drives evaluated in this document: Table 1 - Tape Cartridge Support Matrix Tape Drive Tape Cartridge(s) Supported Compaq 10/20-GB DLT Drive DLT Tape III (10.0-GB) 13 Results including Compaq QIC and DAT tape drives were covered in the previous paper, Compaq Backup and Recovery with Microsoft SQL Server, document #184489-001. 14 The 35/70-GB DLT has an 8 MB on-board memory buffer. 1997 Compaq Computer Corporation, All Rights Reserved Doc No 444A/0797