Rules for mixing HDD types in aggregates

You can mix disks from different loops or stacks within the same aggregate. Depending on the value of the raid.disktype.enable option, you can mix certain types of HDDs within the same aggregate, but some disk type combinations are more desirable than others.

When the raid.disktype.enable option is set to on, single-tier aggregates can be composed of only one Data ONTAP disk type. This setting ensures that your aggregates are homogeneous and requires that you provide sufficient spare disks for every disk type in use in your system.

The default value for the raid.disktype.enable option is off, to allow mixing disk types. For this setting, the following Data ONTAP disk types are considered to be equivalent for the purposes of creating and adding to aggregates, and spare management:

•	BSAS, SATA, and ATA

•	FCAL and SAS

To maximize aggregate performance, and for easier storage administration, you should avoid mixing FC-AL-connected and SAS-connected disks in the same aggregate. This is because of the performance mismatch between FC-AL-connected disk shelves and SAS-connected disk shelves. When you mix these connection architectures in the same aggregate, the performance of the aggregate is limited by the presence of the FC-AL-connected disk shelves, even though some of the data is being served from the higher-performing SAS-connected disk shelves.

You can mix the BSAS and SATA disk types without affecting aggregate performance, but mixing the FCAL and SAS disk types, as well as the ATA disk type with either BSAS or SATA, is less desirable.

MSATA disks cannot be mixed with any other disk type in the same aggregate.

Note: If you set the raid.disktype.enable option to on for a system that already contains aggregates with more than one type of HDD, those aggregates continue to function normally and accept both types of HDDs. However, no other aggregates will accept mixed HDD types as long as the raid.disktype.enable option is set to on.

For information about best practices for working with different types of disks, see Technical Report 3437: Storage Best Practices and Resiliency Guide.