Phabricator to JIRA migration

[ROHAN BHATNAGAR]

Hi All,

I am new to JIRA administration and This is the first time I am migrating all the project management activity from Phabricator to JIRA. I am facing below explained issues kindly help with your suggestions:
1. I am exporting a project in a CSV file from phabricator and importing the same in JIRA, in parallel create a project for it.
2. Initially, I created all the users, manually. Considering my team size is small. Hence no LDAP or AD.
3. As soon as I migrate and check under "User Management" I found duplicate IDs got created. As shown in the image attached. 

My question is 
1. What is the best practice to migrate from Phabricator to JIRA?
2. How can I merge both the accounts which are created? As if I try to delete it, it throws an error that N number of task are assigned to a particular user.

[MattS]

Those two users have different user names so are separate in JIRA. CSV imports can create users for you if needed. I generally create the users before hand as you mentioned.