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.mix.hdd.disktype RAID options, you can mix certain types of HDDs within the same aggregate, but some disk type combinations are more desirable than others.

When the appropriate raid.mix.hdd.disktype option is set to off, HDD RAID groups 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.mix.hdd.disktype.performance option is off, to prevent mixing SAS and FCAL disks.

The default value for the raid.mix.hdd.disktype.capacity option is on. For this setting, the BSAS, FSAS, and ATA disk types are considered to be equivalent for the purposes of creating and adding to aggregates, and spare management.

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

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

Note: If you set a raid.mix.hdd.disktype option to off 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 composed of the specified disk type will accept mixed HDD types as long as that option is set to off.

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