Tape vs. Disk – It’s Time for a Truce
Over the past couple of years we’ve heard an enthusiastic debate over whether Tape is dead, obsolete, or simply relegated to some secondary role like regulatory compliance or litigation response. A lot of the “uproar” has been caused by highly vocal deduplication companies marketing their products by creating fear, uncertainty, and doubt (FUD) among users. And why not, since most of these vendors do not have a significant presence in the tape backup market and therefore little to lose?
However, there are companies with legitimate concerns about managing their backup process and the direction they should take. They need to understand what the facts are and why one approach would be superior to another.
With this goal in mind, let’s take a look at two popular backup & recovery devices – the LTO-5 tape drive and the 3.0 TB SATA disk, and see how they compare.
|Average drive cost-per-unit||$1,450||$ 495|
|Typical media cost-per-unit||$54 per tape||N/A|
|Native formatted capacity||1500 GB||3000 GB|
Native sustained transfer rate
|140 MB/s||155 MB/s|
|Data buffer size||256 MB||64 MB|
|Average file access time||56 sec.||12.16 ms|
|Interfaces available||6 Gb/s SAS||6 Gb/s SAS|
|Typical duty cycle||8-hrs/day||24-hrs/day|
AES 256-bit encryption
|AES 256-bit encryption|
|Power consumption – Idle||6.7 Watts||7.4 Watts|
|Power consumption – Typical||23.1 Watts||11.3 Watts|
|Drive MTBF||50,000 hours at 100% duty cycle||1,200,000 hours|
|Non-recoverable Error Rate||1 in 1 × 1017 bits||1 sector 1×1015 bits|
|5-year total for 1.0 Petabyte||$37,495||$165,330|
No surprises here. Simply doing the math indicates the cost to store 1 Petabyte of data for 5-years would be more four times more on spinning disk than on tape media. Granted there are other factors involved in the process, but most offset each other. Both a tape library and a disk array take data center floor space and infrastructure resources. Both consume power and require cooling. Each system must be managed by skilled IT specialists. Deduplication may reduce disk capacity requirements (reducing cost) but so will tape compression and/or increasing the tape drive’s duty cycle from 8 to 12 hours per day. Surprisingly the only major variable over time is the cost of the media, which is heavily weighted in favor of tape.
In the foreseeable future the 4TB SATA disk will make the above calculations somewhat more favorable for the disk drive. However, we expect to see the LTO-6 tape drive in production in the second half of 2012, increasing the tape drive’s sustained transfer rate by 30% and tape media capacity by 47%. This will bring the above tape vs. disk comparison back into close alignment.
The sensible strategy is to develop a backup and recovery system that incorporates both technologies, to capitalize on the strengths of both. Using disk “pools” to aggregate nightly backups (whether deduplicated or not) ensures backup windows can be met, and greatly improves data restoration time. Backing up directly to tape from the “disk pools” allows streaming data to be sustained for maximum performance and transfers data to the lowest-cost media available for long-term archiving, disaster recovery, regulatory compliance, and litigation response.
It’s time this argument to bed. Both tape drives and SATA disk should play a role in a well-designed, highly optimized backup and recovery system. The “war” is over, and for once both combatants won!