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Why is RAID implemented?

(From "Progress Recommendations with RAID" by Mary Cheng, Progress SmartNews, November 1999)

RAID is an acronym applied to disk technology. It originally stood for Redundant Arrays of Inexpensive Disks, but its current usage is accepted as Redundant Arrays of Independent Disks.

RAID is typically implemented to provide:

• Data reliability by replicating data so that it is not destroyed or inaccessible if the disk on which it is stored fails.
• Improved I/O performance by balancing the I/O load across disks.
• Simplify storage management by treating several physical disks as one virtual unit.

What does BDM stand for?

BDM is the initials of the founders of BDM back in 1968. The "D" of BDM is Dallas Howe, who is the President and CEO of BDM. The "B" and the "M" of BDM were very senior people at the University of Saskatchewan in Saskatoon and never actually made it to BDM.

Almost immediately after our founding, we had customers and name recognition and the company name of BDM stuck.

Today, we sometimes say that BDM stands for "Better Data Management"

What is the purpose of the before-image (BI) file?

A transaction consists of any changes to the database. These changes are recorded as notes in the BI file. Once a transaction is committed, it will be written from the BI file to the database.

The purpose of the BI file is to perform crash recovery to recreate lost committed transactions or undo any transactions that have not been committed at the time of a failure. A failure can occur at the user level or the database level and can be as simple as a power outage which causes the user's connection to the database to be abnormally terminated. The database and its associated before-image files should be treated as a single unit. You cannot have one without the other.

What is the purpose of the after-image (AI) file?

After-imaging is a feature of the Progress database which copies any updates to the database in a separate file on preferably a separate disk. When you enable After-imaging, Progress writes notes to the After-image (AI) file(s) that contain a record of all changes to the database. You can use the last backup of the database and the AI files with the roll-forward recovery process to restore the database to the condition it was in before you lost the database. You do not have to reprocess all completed transactions that occurred since the last backup.

Why do we need to add database extents?

All production RxTFC™ databases are defined as "multi-volume". Defining a database as such requires the setup of the database to include database extents.This is done for a variety of reasons including performance benefits and file size restrictions under the UNIX operating system.

With a single volume database the maximum size of the database would be 2GB. When defining a RxTFC™ multi-volume production database we pre-allocate the database to grow to a certain size by defining a fixed number of database extents. Each database extent is set to an optimum size for your environment.

As the database grows and approaches the size that has been pre-configured, warning messages are issued to indicate that the size threshold is approaching. More space is then added to the database (known as database extents) so the database can continue to grow.

What is socket keepalive?

The keepalive socket option is a setting within the UNIX, (or UNIX derivative) operating system. When there is no other activity on a given socket, the socket keepalive feature triggers periodic transmissions to ensure that the interface connection is still operating properly.