is performance degradation when one disk fails. However the disk can be replaced, the missing data restored and performance returned, automatically when a
The major advantage of RAID 5, is its ability to keep the system up and running in the event of a disk failure, no down time, no loss of data with a single disk failure. However, where as in RAID 0, RAID 1, and Enhanced RAID 1, the loss of a single disk may require a reboot of the system; in RAID 5 it does not. This is a major advantage when there is a need to keep the data available to endusers and customers for long periods.
5.2.5.5 IBM ServeRAID Adapters
Today’s business critical data grows at an alarming rate. A few years ago a database of around 20 GB would have been considered large, even beyond the scope and capacity of all but the largest of mainframes.
Today, databases of around 20 GB are very normal, and nothing out of the ordinary. It is databases of 1 or 2 terabytes that are seen as incredibly large.
So what growth rate can you expect from your customer’s database?
The answer is unpredictable, but one point is certain, and that is, grow it most certainly will. If you have a system that will handle up to 100 GB of hard disk today, but you require only 60 GB, your customer will buy 60 GB of hard disk. Sometime in the future, your customer will want to expand, or concentrate some of his data, into smaller more manageable sizes. The challenge is to achieve this data without losing availability to endusers.
So how can this be achieved? Until recently, we had to:
1.Back up all the data.
2.Redefine the disk arrays, or install larger disks and redefine the arrays.
3.Restore the data.
This is an expensive way of growing a database. In today’s environment this would be unacceptable within a 24x7x365 operation.
The IBM ServeRAID adapter has the answer to this. To grow the database as mentioned above from 60 GB to 100 GB, you would simply insert more hard disks, and migrate or "grow instantly" the disk space available to the operating system, by increasing the size of the array that is already in use, without any loss of service to endusers.
With IBM ServeRAID adapters, you can migrate the data in a variety of ways. The options are:
•From RAID 0 to RAID 5
•From RAID 5 to RAID 0
•From RAID 1 to RAID 5
•From RAID 5 to RAID 5 (array expansion)
This functionality of the IBM ServeRAID adapter is known as Logical Drive Migration (LDM) and is available as standard with all current IBM ServeRAID
42J.D. Edwards’ OneWorld B73.3 and Windows Terminal Server
