E01 indicates the second storage group on a server.
E02 indicates the third storage group on a server.
etc.
First Storage Group
Tmp.edb
As the name indicates, it is temporary. During information maintenance, tmp.edb is used for transient storage. When the indexes are created and when data are sorted, tmp.edb is used.
E00RES00001.JRS and E00RES00002.JRS reserve a portion of disk space. In case the hard disk full, these two files allow the Exchange 2007 to shutdown normally instead of crashing the system.
E00.log is the current transaction log. Exchange first writes data to this log file. When E00.log is full, it is renamed according to the format E00000000001.log, E00000000002.log, etc.
E00tmp.log
Because renaming E00.log and creating a new E00.log takes some time, it is highly possible that Exchange 2007 has new data to be logged. E00tmp.log file bridges the gap. The new data is stored in E00tmp.log file.
E00.chk
It is a checkpoint file. At a given moment, not all the transactions in log files (E00.log, E00000000001.log, etc.) are committed to database file Mailbox Database.edb. The E00.chk marks the point at which the transactions are committed.
