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March 29, 2011

Keeping up with Storage Technology

While I was at SHARE a few weeks ago, I listened to IBM discuss BIG DATA and the evolution of data storage from terabytes to petabytes to exatabytes to zetabytes. As I thought about supporting these unimaginably huge numbers, I wondered further about the enhancements to storage technology and how DB2 for z/OS benefits from these changes.

Click the following link to download "Bytes Table:"  Download Bytes Table

DB2 for z/OS uses features in the Data Facility Storage Management Subsystem (DFSMS) to take advantage of improvements in both software and hardware interfaces. One area of improvement is in the size of volumes supported. The largest traditional 3390 device, 3390-54, supports 65,520 cylinders or approximately 54 GB. z/OS V1R10 introduced Extended Address Volumes (EAV), which raised the volume size to 262,668 cylinders, or 223 GB.

To give you an idea of the progression in size by device:

3390-3      Max cyls:     3,339        3GB
3390-9      Max cyls:   10,017         9GB
3390-27    Max cyls:   32,760      27GB
3390-54    Max cyls:   65,520      54GB
3390-A     Max cyls:   262,668    225TB

As you can imagine, having more datasets on one volume can increase the I/O queue time. Old-time DBAs spent many hours determining the best dataset placement and separation across I/O controllers to avoid I/O bottlenecks. Now this issue is addressed by configuring an EAV device to use parallel access volumes (PAVs). PAVs bring a significant performance improvement over traditional I/O processing by allowing a single device from a single host to process multiple concurrent requests. When you PAV-enable a logical volume, you assign a static number of PAVs to that volume. However, you may find that you can't assign enough PAVs to keep up with the workload for a given volume. To address this issue, the DS8000 series disk subsystem offers an enhanced PAV with support for HyperPAV, which provides equal or better I/O performance while using the same or fewer operating system resources.

I’m sure your storage administrator can explain it in more detail than I just did. Storage has and will continue to be enhanced in many ways that make a DBA's job easier. Take the time to learn about these new technologies. And if the latest storage technologies are already in use at your company, please share a bit about your experiences in Comments.