by November 10, 2003 0 comments



Once you’ve identified your business requirement, choosing the right tape technology comes next. Here, there are several key issues that need attention. These include the following: 

Tape capacity: Tape manufacturers usually specify two separate capacities for their tapes: native capacity and compressed capacity. Native capacity is the actual available capacity on the media. But, most tape drives use some algorithm to compress data before writing it to tape. This increases the overall available capacity. Here, the actual compression depends on the kind of data being stored and will therefore not always be equal to the manufacturers’ rating. For example, .bmp and text files are more compressible than binary or .exe files. So, while choosing a backup solution, look for the uncompressed (the native) capacity.

Speed of writing data on tape: This becomes important when you have lots of data to back up, and would like to have it backed up in the shortest time possible. The capacity and speed would depend upon the tape technology you choose. The speeds range from 1.2 MB/sec to 30 MB/sec. 

Compatibility and future roadmap: The third most important thing while choosing a backup solution is compatibility, both backward and forward. Backward compatibility implies that newer tape drives will support older formats. For example, whether the new DDS-4 drives will support older DDS-3 format. If it doesn’t and you already have all your data backed up in DDS-3 format, then you would have to move all data to the new format if you go for it. That adds to your running cost. Forward compatibility is even more important. While selecting a solution for your present needs, it is essential to see, whether it will be supported, say a few years down the line. Otherwise, you’ll again have to move all your data to the next new technology. Therefore, check for the roadmap of the backup technology you’re planning to go for.

Drive maintenance and service: This is the next level. All tape cartridges have a usable life and a shelf life, depending upon whether you’re using it for backup or archival. So you’ll need to see how soon would you have to replace the cartridges of the technology you choose and what the replacement cost will be. 

Interface and form factor: While SCSI is the favorable choice for connecting tape drives, IDE and USB tape devices are also available. SCSI, with so many standards may also crop up installation or performance issues. Apart from the interface, things like the size of the tape and drive, whether it’s internal or external, should be considered.

Cost: Last but not the least is the cost at which you get the entire solution. This includes both the price of the drive and the cartridges. The latter is important as it’s the running cost. It would vary because the number of cartridges you’ll use will vary depending upon your back up strategy.

Popular tape technologies
We have checked out ten drives using four different tape technologies: DDS, AIT, DLT, and LTO-ULTRIUM. We’ll first give an overview of the various technologies, followed by how they actually performed in our tests. 

DDS/DAT
DDS or Digital Data Storage is a computer data storage format based on an earlier DAT (Digital Audio Tape) format, used for Digital Audio. Developed by HP and Sony, DDS tapes are also available from Fujifilm, Imation and Exabyte. DDS has gone through four different revisions: DDS, DDS-2, DDS-3, DDS-4; the first two formats are not used as much as the others now. HP has further revised this standard and calls the latest standard DAT 72. DDS cartridges have an archival storage life of 10-20 years and a usage life of about 2000 end-to-end passes. DDS cartridges are quite smaller in size and lightweight compared to other formats.

DDS-3: capacity 12GB native, 1.2MB/sec native transfer rate
DDS-4: capacity 20GB native, 2.4MB/sec native transfer rate
DAT72: capacity 36GB native, 3MB/sec native transfer rate 

DDS format is backward compatible with all previous formats, but it does not have a well defined future roadmap, especially when HP has moved away from the name DDS, with its latest DAT72 tapes.

AIT
AIT is Advanced Intelligent Tape format developed and widely supported by Sony. Others like HP, Fujifilm and Exabyte also have products based on this format. Currently AIT has three generations and one advanced Super-AIT. AIT tapes have an archival life of 30 years and a usage life of 30,000 end- to-end passes. In size, AIT cartridges are bigger than DDS but smaller than DLT and
LTO-ULTRIUM.

AIT-1: capacity 35GB native, 4.0MB/sec native transfer rate 
AIT-2: capacity 50GB native, 6.0MB/sec native transfer rate
AIT-3: capacity 100GB native, 12.0MB/sec native transfer rate

Like the DDS format, AIT is also backward compatible with previous generations. Presently the future roadmap is also well defined up to AIT-6 to arrive by 2007.

DLT
DLT or Digital Linear Tape is supported largely by Quantum but HP, Dell, IBM, Fujifilm, Maxell and Exabyte, also provide DLT products. Like other formats, DLT also has several generations DLT III, DLT IV, DLT VS1. Out of these, DLT IV is the most commonly used. Archival life of DLT media is 30 years and about 1,000,000 end to end passes usage life. DLT tape cartridges are bigger in size than AIT and DDS and
LTO-ULTRIUM.

DLT IV: capacity 40GB native, 3.0 – 6.0 MB/sec native transfer rate.

All DLT formats are backward compatible and the future roadmap is also properly laid out up to DLT VS600 with 600GB capacity.

LTO-ULTRIUM
LTO or Linear Tape Open was jointly developed by HP, IBM and Seagate, and Ultrium is one of the two formats based on this technology. The other is Accelis. Ultrium has two generations Ultrium-1 and Ultrium-2, with the latter being the latest. Archival life is more than 30 years and usage life about the same as DLT. Ultrium cartridges are slightly smaller in size than DLT cartridges.

Ultrium-2: capacity 200GB native, 30MB/sec native rate.

The future roadmap has been laid out till generation 4 with about 1.6 TB capacity.

These aren’t, of course, the only tape technologies available. There’s the super DLT format, which is the next
big upgrade to DLT, ADR (Advanced Digital Recording), SLR (Scalable Linear Recording), VXA, Mammoth, Travan and
Accelis.

Anoop Mangla

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