Century IT blog

60 Second Cram of tape drive capacities

December 7th, 2008

203_tandberg-lto-2-hh-external-drive-frontDDS/DAT Drives

DDS1   2GB/4GB

DDS2   8GB/16GB

DDS3   12GB/24GB

DDS4   20GB/40GB

DDS5   36GB/72GB

DDS6   80/160GB


AIT Drives

AIT1   40Gb/100GB196_vxa-220external20drive

AIT2   80GB/200GB

AIT3   100GB/260GB


LTO/Ultrium Drives

LTO1   100GB/200GB

LTO2   200GB/400GB

LTO3   400Gb/800GB

LTO4   800Gb/1600GB


Tape drive compression (confusion)

 All tape drive manufacturers list 2 capacity figures in the specification of their tape drives, a lower capacity and a higher capacity. This is confusing and catches a lot of people out.


For example a DAT72 might imply it can backup 72GB of data to tape, but in the real world you could expect to see probably somewhere between 40-55GB of data being backed up.

Again a Ultrium 100GB/200GB might imply that you could backup 200GB of data onto tape, in the real world you might expect to see probably somewhere between 130GB to 160GB of data going to tape.


Why is this? It is important to remember that the reason 2 different capacity values are listed is due to the type of technology used in these modern tape drive’s hardware. The lower capacity value is generally the guaranteed capacity. The higher value can be misleading, but basically modern tape drives use compression. As data is transferred to tape, the tape drive hardware will compress data in order to use the tape media more efficiently.


Different types of data can compress at different rates. I.e. databases can be compressed more efficiently than say pictures or mp3s.


The higher capacity rating is generally the total capacity of the tape drive assuming — it can compress all your data at a 2:1 ratio. We all live in the real world where we can have a range of different applications and data stored on our computer systems, in our experience the higher capacity has never been attained and you should not rely on the higher compressed capacity to backup all of your data.



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