RAID groups are a crucial part of the underlying structure of your storage infrastructure, which makes understanding them as important as any other component of your data center. To help you better understand the differences between the different RAID group levels and benefits of choosing one level over another, we’ll start with the core definition. The acronym RAID stands for “Redundant Array of Independent Disks” and is most frequently used for storing the same data in multiple places or on various hard drives while still having good performance. Aside from just understanding what “RAID” means by its definition, it is vital to know how RAID groups fit into your larger data center infrastructure.

What Do You Need In Order To Make a RAID Group?

RAID groups are made up of a collection of disks and RAID groups can be used to create storage pools. So, before building your RAID groups you should understand your data center needs and find out what would work best for you. Choosing the type and number of drives to build your RAID group will vary based on the workload. Think about what you’ll be using this RAID group for. Will it be used to hold data that will be accessed frequently? That will affect the drives on which you choose to base your RAID group. For a system such as the VNX5300, you’ll choose from the following drive types: Flash/SSD, SAS, or NL-SAS.

Which Disk Drive Type is Best for My RAID Group?

Flash is the fastest drive out of the three named above. Flash drives will give you the most Input/Output Operations Per Second (IOPS). SAS is often used as a “sweet spot” drive type because it provides a range of sizes while still providing good IOPS speed of around 180. NL-SAS is known more for its capacity, but not speed, so this drive type is more frequently used for archiving data that isn’t accessed frequently. So, once you understand your workload, you can choose the best drive type for those performance requirements. Then you’ll need to choose the RAID level for those drives.

What Are the Different RAID Levels?

There are multiple RAID levels available for RAID groups. These different RAID levels provide a different type of performance and can affect data center performance. Essentially, RAID levels can allow you to have spares and redundancy as well as techniques such as mirroring and parity striping in order to save data in multiple places. Choosing the best RAID level for your organization and performance needs may vary based on the manufacturer of the equipment you are using, but for the sake of this blog, we’ll use RAID 5, RAID 6 (DP), and RAID 10/RAID 1+0 as examples.

RAID 5: RAID 5 gives you 5 drives and allows you to have one parity drive. The parity or parity striping allows you to distribute data to all disks in the RAID group. In RAID 5, the parity allows you to lose one drive without losing any data in that RAID group because each disk knows what the other disk holds.

RAID 6 DP: RAID 6 DP, or dual parity, is somewhat different from other RAID levels. The main difference is that this RAID level includes two parity drives, or dual parity, which allows you to lose up to two drives without losing any data on that RAID group.

RAID 1+0: RAID 10 or RAID 1+0 employs the mirroring technique as well as parity striping across all of the drives in the RAID set. One of the pros of this RAID level is as long as you have one drive in all of the mirrored pairs you won’t lose any data. On the other side, you’ll only have 50% of your raw capacity to use due to mirroring.

Parity vs. Spare

When learning about parity striping it is equally important to understand spares. Spares for your RAID group have the same purpose as a spare tire for a car, you have it just in case you need it. Parity drives and spares have similar functions in the way that they provide an extra layer of protection against losing data. For example, say you’re using RAID 5 and one of your drives has a media error or it meets its threshold then what happens is the drive “proactively copies” its data to the spare. That’s when the spare comes in and takes over that drive you lost allowing you to keep all of your data. The parity drive has the same outcome but it comes into play when there’s an issue in your data center. If there’s a mechanical failure in the RAID group and the drive can’t proactively copy the data to the spare that’s why parity striping is there. Like previously stated, parity striping allows you to distribute the same data onto multiple drives.

Now What?

Now that you understand the terminology around RAID levels and RAID groups you can look into creating a pool of RAID groups. Pool creation allows you to mix RAID groups made up of different drive types in one pool. So, you can combine Flash, SAS, and NL-SAS in one place to get the best performance out of your data center. Still have questions around RAID groups, levels, or storage pool creation? Reach out to Reliant Technology now to chat with a storage specialist or give us a call at 1.877.227.0828