This is actually the continuation my previous update on the server. As I noted in that previous post setting up a RAID 5 with six 146 GB drives and two 72 GB drives was very stupid. But I never explained why this is a stupid idea on my first post. Today we will look at the best way to mix and match different types of harddrives on a RAID system for optimum performance and the highest storage output.
The the RAID 5 system works by taking all the hard drives with even different sizes and strip the data on all of them to provide one drive fail backup support for the system. In other words, on a RAID 5 system, you an tolerate one drive failure without loosing data. In this method, the RAID controller will take the lowest capacity of all the drives on the array and multiply that lowest capacity by the number for drives regardless of the capacities of the larger drives. For example, if we have two 72 GB drives and six 146 GB drives, the RAID controller will see all the eight drives as 72 GB drives. By doing the math for the RAID 5 system: (72 GB * 8)-72GB = 567 GB in total. Considering 146 GB *6 itself is 876 GB, this creates a a lot of wasted space. In addition to this reduced space, the 72 GB HDs are running at 15K RPM while the 146 GB HDs are running at 10 K causing the RAID to operate at the lowest RPM value of 10 K even with the six 15 K drives have the capability to read and write at faster speeds.
Solution when you want to mix and match? Create two (or more) different independent RAID systems! By dismounting the RAID 5 configuration of mixed drives and rebuilding two independent RAIDs, one with the six 147 GB at 10 K drives as a RAID 5 and the other two 72 GB at 15 K as a separate RAID 1, you can get the maximum performance and the maximum storage capacity for the buck. The OS is loaded to the 75 GB drives on RAID 1 giving it faster speeds to boot up and perform operations for the server as well as top class redundancy. This is a lot more than space to load the OS, most of the server roles, and other applications. The slower side with RAID 5 yielded about 682 GB after formatting. The theoretical yield can be calculated as: (146 GB *6)-146GB = 730 GB. This is about theoretical value of 163 GB more than what I was able to get from all eight hard drives in RAID 5 configuration.
This new system also have another advantage when it comes to RAID drive failures. The RAID 5 and RAID 1 are independent of each other. The RAID 1 has the capacity to protect data up to one fail drive and the RIAD 5 also offer the same one drive fail safety! Also for future upgrade to the system on the RAID 5 side can be done without loosing the OS updates and applications stored in the RAID 1 side of the server.
Why didn’t I think of this before?