When 2x RAID 5 = RAID 10

An occasion I will never, ever forget is the time I set foot in a small business and the developers and IT Manager alike told me how their database server was in RAID 10. They spoke at length about the research they put in to determine the most performant disk configuration and came to the determination RAID 10 was best for their requirements.

The old adage, “what gets measured gets improved” is equally true in reverse; what doesn’t get measured doesn’t get improved. Noting the database was a key component of the company’s business, and that no reporting or analysis was occurring, I recommended several tools such as the free open-source dbWarden script. I speak more about this and other good, even essential, tools for keeping your database healthy over on iTWire.

The results were not good! In fact, there was significant lag. The database server was spending most of its time waiting to write – adding up to minutes every day, and many queries were taking over 100ms.

I asked the IT Manager to show me the disk setup. He took me into the server room and entered the server’s RAID configuration. Two RAID 5 volumes. We looked at each other, and he immediately said, “This was RAID 10! The systems administrator must have changed it!”

He asked that person if he changed it, he said no, that’s how it has always been. The IT Manager, never short for an answer, then confidently explained the server had been ordered from Dell as a database server so Dell “must” have pre-configured it according to their best practice.

It got worse.

Within Windows, one of the RAID 5 volumes was used exclusively for drive E:, which contained nothing but the Windows pagefile.

The other RAID 5 volume was partitioned within Windows as C: and D:. The operating system, the application, the database and the log files were all on the one RAID 5 volume albeit two Windows partitions.

Oh, and there were also a bunch of file shares, used by the most prolific file-heavy section of the business sitting on D: also.

You can be sure I made a series of recommendations, not only relating to infrastructure configuration but about staffing too.