Disk and Tape Square Off Again Tape Remains King of Hill with LTO-4 Presented by Heba Saadeldeen

1. Disk and Tape Square Off Again Tape Remains King of Hill with LTO-4 Presented by Heba Saadeldeen

2. Goal • Decide whether the decreasing costs of disk subsystems and the increasing capacity of disk drives might have made the TCO for disk more attractive versus tape in the long-term storage of data. • Study Period : 5 years. • Size of enterprise: Data center of a mid-sized business

3. How do they compare the cost of both disk and tape storage ? • Store the 90 days worth of backup data on a disk (disk cache) to help meet the performance objectives defined in service level agreements. • We will then save the 13th weekly full backup as the archived quarterly backup and save it to a disk system and to a tape system – to compare the TCO costs of each long- term storage solution . • The cost comparison, over five years focuses on storing these “archived quarterly backups” on the two alternatives, disk and tape .

4. Findings • For long term storage, over the five year study period, the cost of disk is about 23 times that of the tape. • The cost of energy is 290 times that of tape

5. Assumptions • Tape assumptions • Disk assumptions • Energy assumptions

6. Tape Assumptions • Use LTO-4 • It was released in 2008. • Doubled capacity again to 800 GB. • Use standard compression ratio of 2:1 • Increase data transfer rate by 50% to be 120 MB/s • Tapes retire every 5 years. • Use N+1 tape drive to ensure device availability. N is the number of tapes required to complete backup.

7. Disk Assumptions • 750GB SATA disk drives • Disk retire every 3 year

8. Energy Assumptions • Use an average urban rate ($0.12/KWH). • Assume that the energy cost is constant throughout the entire period of study • A dollar to cool the environment for each dollar spent to run the data center's infrastructure.

9. Cost Model • Includes: • Equipment • Media • Energy • Floor space requirements

10. Storage Requirements

11. Disk Cost

12. Energy Consumption for Disk • Assume that typical power usage for a normal system operation consumes 11,000 WPH. • Use conservative power rate = $0.12/KWH • Assume that the energy for cooling = energy for operation

13. Disk Cost (cont.)‏

14. Disk Cost (cont.)‏

15. Conclusion for Disks • The H/W cost dominates the total cost. • Energy and space consumes only 4% of the total cost. • This cost model does not include cost of administration or backup software.

16. Tape Cost

17. Energy Consumption for Tape • The active tape library, without drives, consumes 185 Watts per hour • Each additional frame adds 110 watts • Each active LTO-4 drive, power supply, and associated infrastructure consumes about 50 watts while reading/writing, 12 watts when idle • The initial deployment of library with two drives will consume 1150KWH in the first year

18. Tape Cost (cont.)‏

19. Conclusions • All of one solution does not work. • Disk cache is still required to meet SLA. • Tape is not dead for archival storage. • Hardware cost dominates.