Hello, I have a question, I have two servers in 7.2, we are going to upload one of them to 7.4, but we have doubts if there will be any problem with DDMs or with other communication things between 7.4 and 7.2. What problems could we find?
(At some point we're going to have to upgrade the other server to 7.4 but while we're at it we need to check out this environment)

Dear Miguel

In general, sending data from lower IBM release server to a higher release one should be fine. It's the other way round that may  encounter problem if you are dealing with objects (like saving objects to a save file and FTP the save file and restore from it - Target Release parameter takes care of this issue but once in a blue moon, rare problem (that I cannot remember now as it was rare) can occur).   If you are dealing with data rows such as remote SQL (DRDA) or DDM file, there should be no issue accessing data both ways between the two releases.   

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Education is not the learning of facts but the training of the mind to think. -- Albert Einstein.
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Satid S.
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Nothing immediately comes to mind.  Although we tend to try to get everything to the same release ASAP.

Read both the 7.3 and the 7.4 information at the following.  Do not skip reading the 7.3 information as 7.4 doesn't repeat all the stuff which changed in 7.3.

https://www.ibm.com/docs/en/ssw_ibm_i_74/pdf/rzaq9.pdf

https://www.ibm.com/docs/en/ssw_ibm_i_73/pdf/rzaq9.pdf

https://www.ibm.com/support/pages/node/668149

https://www.ibm.com/support/pages/node/880105