Loss of database transaction logs
Failure of the non-redundant internal disk can result in the loss of transaction data in the database which can result in loss of transaction data.
A database management system (DBMS), like Oracle and Db2®, guarantees the integrity of the data. When a transaction commits its work, the DBMS guarantees that all the changes are either in the database disks, or can be recovered from transaction logs.
When a database instance crashes, the DBMS is designed to automatically perform "rollforward or instance recovery". Therefore, when you restart the instance, the DBMS will ensure that "committed" changes in its retransaction log are applied to the database files. Similarly, if you had to recover the database from backup, you could also initiate a rollforward recovery from the transaction logs to reapply all the transactions since the backup was taken.
The loss of the transaction logs typically means that at best, the DBMS cannot perform rollforward recovery and at worse, you have to recover the database from the last backup. In either case, this system could lose transaction data.
Never place transaction logs or database files on non-redundant internal disks. These critical files should be placed on redundant storage devices.