Tape: Alive and full of options


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Tape Media Formats
DLT: Ranges in capacity from 10GB native/20GB compressed (DLT III) to 40GB native/80GB compressed (DLT IV). The older DLT III tapes have a shelf life of more than 20 years, while the latest DLT IV technology extends the life of the tape to more than 30 years. All DLT tapes are readable by the latest SDLT tape drive technology.
SDLT: Represents the current generation of DLT tapes. The

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SDLT 220 has a capacity of 110GB native/220GB compressed while the latest SDLT tape cartridge--the SDLT 320--holds 160GB native/320 compressed. The SDLT 320 media supports compressed transfer rates of up to 32MB/s and SDLT tape drives are capable of reading, but not writing to, older DLT tape media. SDLT tape media also have a life expectancy of more than 30 years. DLT and SDLT have combined to sell over 90 million cartridges and two million tape drives.
LTO Ultrium: Jointly designed by HP, IBM, and Seagate and is a relative newcomer to the tape space, first being introduced in 2000. The most current product shipping supports 200GB native/400GB compressed, supporting a tape drive throughput speed of 35MB/s native and 70MB/s compressed. IBM estimates a shelf life of up to 30 years for LTO Ultrium tapes and has already shipped over five million LTO cartridges in just a little over three years.
AIT: First introduced into the market in 1996 with three formats currently available on the market: AIT-1, AIT-2 and AIT-3. AIT-3 natively supports drive capacities of 100GB and with a higher than average industry compression rate of 2.6:1, gives it a compressed capacity of 260GB. It offers a transfer rate of 12MB/s native, 31MB/s compressed.
Next-generation tapes: Brings still higher capacities and faster throughput to the marketplace. The SDLT 600 tape cartridges are due out Q4 of 2003 with compressed capacities of 600GB and 64MB/s throughput rates. The 2006 forecast for the SDLT 2400 anticipates over 200MB/s throughput and 2TB of data compressed on a single tape media. Both LTO Ultrium and AIT include similar high transfer rates and media storage forecasts in their roadmap over the next one to three years. For instance, SAIT-1--released February 2003 by Sony--became the first tape media to break the 1TB barrier with the ability to store 1.3TB compressed (assuming a 2.6:1 ratio) on a single tape. Sony anticipates tape library solutions from vendors such as Qualstar will possibly be available as soon as spring 2003 to support this new format.

Where's tape headed?
Now that I've listed many of the technical advances in today's tape libraries we should address that age-old argument: Tape is dead. Nothing could be further from the truth.

IBM's Bruce Master believes that the cost of tape still beats the cost of disk by a long shot. Despite the recent price drops of low- cost disk to under a penny a MB, tape media is still less expensive by a wide margin. Future IBM tape technology, he says, could hold a terabyte of data on just one tape, which equates to about ten cents a gigabyte. HP's Luttrall adds that no matter how much the cost of disk drops, disk cost will still exceed the cost of tape by ratios ranging from 20:1 to 50:1.

Yet none of the tape vendors dispute the value of disk in the next generation of backup solutions. In fact, HP sees disk as a critical piece of their multilevel data protection strategy and views technologies such as ATA arrays as being complementary solutions to tape, serving as a disk cache in front of tape to stage the data prior to being backed off to tape. Some of the tape libraries on the market have already capitalized on this idea. In 1997, IBM introduced their Virtual Tape Server that uses disk to present a virtual tape subsystem to the host system. While primarily in use on the mainframe, it's has crept into a few open systems environments and IBM foresees this technology growing in the future.

Another area where tape outshines disk is in offline storage, because tape is portable and removable. HP's Luttrall says that when data remains online as it does in the case of disk, it remains vulnerable to corruption. Tape, on the other hand, can be moved and vaulted. While this introduces some management costs and a potential for tape destruction or loss, it also protects the data from human error--accidental or malicious. It also allows the data to be moved offsite in case of outage or disaster where the primary data facility resides.

Finally, tape just flat out outperforms disk in its ability to read and write data sequentially. Many of today's tape libraries may host anywhere from 16 to 400 tape drives. Couple this number of tape drives with new tape drive technologies now supporting speeds of over 30MB/s and it adds up to backup speeds that disk simply can't match.

Consolidate or eliminate?
Should you consolidate all your tape libraries down to one or standardize on a tape library that only handles one tape format? A case can be made for each approach.

The argument for putting all of the tape mediums into one tape library sounds compelling: Place all your tape mediums into the one library and then verify compatibility with backup software products. This contrasts with standardizing on one tape medium. However, any library that reads multiple tape formats has its downsides: It's more expensive and has more management complexity. If you throw AIT or SDLT tape drives into the mix, your backup speeds and times will vary and you'll always be asking which application is backed up on what tape format. In addition, each of the tape mediums will have different life expectancies and handling requirements, whereas with only one tape format, you'll only have--at most--two or three variables.

In either scenario, you have a major management headache. In the case of a single tape format, there's the pain and expense of moving data to that solution. In the case of multiple tape mediums, you may end up chasing your tail trying to figure out which application is backed up by what type of tape media. The bottom line: The costs of the actual physical devices probably evens out and the ability to manage the environment becomes the key long-term differentiator.

This was first published in April 2003

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