This is from http://h18006.www1.hp.com/products/quickspecs/11529_div/11529_div.html


Backward Read Compatible                   LTO1 Drive       LTO2 Drive      LTO3 Drive      LTO4 Drive
                            LTO1 Media     Read/Write       Read/Write      Read Only       Not Compatible
                            LTO2 Media     Not Compatible   Read/Write      Read/Write      Read Only
                            LTO3 Media     Not Compatible   Not Compatible  Read/Write      Read/Write
                            LTO4 Media     Not Compatible   Not Compatible  Not Compatible  Read/Write

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This is from http://www.quantum.com/products/tapedrives/ltoultrium/index.aspx

 MEDIA COMPATIBILITY     
 

Quantum LTO-2 HH tape drives write to the following media:
LTO Ultrium 2 (MR-L2MQN-01/Old PN CLM400), LTO Ultrium 1 (MR-L1MQN-01/Old PN CLM200)

Quantum LTO-2 HH tape drives read the following media:
LTO Ultrium 2 (MR-L2MQN-01/Old PN CLM400), LTO Ultrium 1 (MR-L1MQN-01/Old PN CLM200)

Quantum LTO-2 HH tape drives utilize the following cleaning cartridge:
LTO Universal (MR-LUCQN-01/Old PN CLMCL)
 


 MEDIA COMPATIBILITY     


Quantum LTO-3 HH tape drives write to the following media:
LTO Ultrium 3 (MR-L3MQN-01), LTO Ultrium 2 (MR-L2MQN-01)

Quantum LTO-3 HH tape drives read the following media:
LTO Ultrium 3 (MR-L3MQN-01), LTO Ultrium 2 (MR-L2MQN-01), LTO Ultrium 1 (MR-L1MQN-01)

Quantum LTO-3 HH tape drives utilize the following cleaning cartridge:
LTO Universal (MR-LUCQN-01)

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When using LTOx media, the capacity will be based on LTOx formatting.  If you use LTO2 media in an LT03, you will only get 200GB native (or 400GB with 2/1 compression), not the 400GB native capacity (800GB with 2/1 compression) you will get with LT03 media in an LT03 drive.