What exactly are iblog files in mysql
ibdata1

The file ibdata1 is the system tablespace for the InnoDB infrastructure.

It contains several classes for information vital for InnoDB


Table Data Pages
Table Index Pages
Data Dictionary
MVCC Control Data


Undo Space
Rollback Segments

Double Write Buffer (Pages Written in the Background to avoid OS caching)
Insert Buffer (Changes to Secondary Indexes)


Click Here to see a Pictorial Representation

You can divorce Data and Index Pages from ibdata1 by enabling innodb_file_per_table. This will cause any newly created InnoDB table to store data and index pages in an external .ibd file.

Example


datadir is /var/lib/mysql
CREATE TABLE mydb.mytable (...) ENGINE=InnoDB;, creates /var/lib/mysql/mydb/mytable.frm


innodb_file_per_table enabled, Data/Index Pages Stored in /var/lib/mysql/mydb/mytable.ibd
innodb_file_per_table disabled, Data/Index Pages Stored in ibdata1



No matter where the InnoDB table is stored, InnoDB's functionality requires looking for table metadata and storing and retrieving MVCC info to support ACID compliance and Transaction Isolation.

Here are my past articles on separating table data and indexes from ibdata1


Oct 29, 2010 : My Original Post in StackOverflow
Nov 26, 2011 : ERROR 1114 (HY000) at line 6308 in file &amp; The table user_analysis is full
Feb 03, 2012 : Scheduled optimization of tables in MySQL InnoDB
Mar 25, 2012 : Why does InnoDB store all databases in one file?
Apr 01, 2012 : Is innodb_file_per_table advisable?


iblog files (a.k.a. ib_logfile0, ib_logfile1)

If you want to know what the ib_logfile0 and ib_logfile1 are for, they are the InnoDB Redo Logs. They should never be erased or resized until a full normal shutdown of mysqld has taken place. If mysqld ever crashes, just start up mysqld. It will read across ib_logfile0 and ib_logfile1 to check for any data changes that were not posted to the the double write buffer in ibdata1. It will replay (redo) those changes. Once they are replayed and stored, mysqld becomes ready for new DB Connections.