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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, single-tier aggregates and the HDD tier of Flash Pool 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.mix.hdd.disktype.performance option is off, to prevent mixing SAS and FC-AL disks.

The default value for the raid.mix.hdd.disktype.capacity option is on. For this setting, the SATA, 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-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.

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

Disks using Storage Encryption have a Data ONTAP disk type of SAS. However, they cannot be mixed with any other disk type, including SAS disks that are not using Storage Encryption. If any disks on a storage system use Storage Encryption, all of the disks on the storage system (and its high-availability partner node) must use Storage Encryption.

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.