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.

  Specification Quantum Internal
half-high LTO-5
Seagate Constellation
ES.2 ST33000651SS
  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
  Encryption
AES 256-bit encryption
AES 256-bit encryption
  Power
  Power consumption – Idle 6.7 Watts 7.4 Watts
  Power consumption – Typical 23.1 Watts 11.3 Watts
  Reliability
  Drive MTBF        50,000 hours at          100% duty cycle 1,200,000 hours
  Media MTBF 30-yrs
  Non-recoverable Error Rate 1 in 1 × 1017 bits 1 sector 1×1015 bits
  Warranty 3-Year 3-Year
  Cost Comparison
  Storage Cost-per-GB $0.036 $0.165
  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!

About Big Data Challenges

Mr. Randy Cochran is a Senior Storage Architect at Data Center Enhancements Inc.. He has over 42-years of experience as an IT professional, with specific expertise in large and complex SAN/NAS/DAS storage architectures. He is recoginzed as a Subject Matter Expert in the enterprise storage field. For the past five years his primary focus has been on addressing the operational requirements and challenges presented by petabyte-level storage.

Posted on June 10, 2012, in Backup & Recovery and tagged , , , , , , , . Bookmark the permalink. 7 Comments.

  1. Thanks for your response. The numbers are all-inclusive estimates taken from a data center environment where capacity, power, cooling, floorspace, management, security, equipment lifetime, etc., etc. all go into the calculation. It gives a far more accurate apples-to-apples comparison than just looking at street prices for drive units.

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