I have multiple T1 cards on the Asterisk Server. How do I know which T1 card will load first?

Ans: This is very important question as SPANs for Tie Trunks relates with the order in which T1 card loads. For example,
Card 0 has Span1-4 as it is loaded first
Card 1 has Span5-8 as it is loaded second

However, what will happen if Card1 loads first. You are in trouble as Card1 will host Span1-4, not the Card0.

To prevent this disaster to happen, Digium has Ident Dial that makes the driver load on the card in specific order. Ident Dial has range from '0-9' 'A-F'.

Now, I would do this

Card0 with Ident set to 0
Card1 with Ident set to 1

This will ensure that Card0 will have Span1-4
and Card1 will have Span5-8

Setting all cards to zero should cause the driver to automatically number the cards. The dial should only be used if a specific order is needed.

http://kb.digium.com/entry/106/