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System Manager Classic

How System Manager works with hot spares - ONTAP 9.7 and earlier

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A hot spare is a disk that is assigned to a storage system but not used by any RAID group. Hot spares do not contain any data and are assigned to a RAID group when a disk failure occurs in the RAID group. ONTAP System Manager classic (available in ONTAP 9.7 and earlier) uses the largest disk as the hot spare.

When there are different disk types in the RAID group, the largest-sized disk of each disk type is left as the hot spare. For example, if there are 10 SATA disks and 10 SAS disks in the RAID group, the largest-sized SATA disk and the largest-sized SAS disk are serve as hot spares.

If the largest-sized disk is partitioned, then the hot spares are provided separately for partitioned and non-partitioned RAID groups. If the largest-sized disk is unpartitioned, then a single spare disk is provided.

The largest-sized non-partitioned disk is left as a hot spare if there are root partitions in the disk group. When a non-partitioned disk of the same size is not available, then spare root partitions are left as hot spares for the root partitioned group.

A single spare disk can serve as a hot spare for multiple RAID groups. System Manager calculates the hot spares based on the value set in the option raid.min_spare_count at the node level. For example, if there are 10 SSDs in an SSD RAID group and the option raid.min_spare_count is set to 1 at the node level, System Manager leaves 1 SSD as the hot spare and uses the other 9 SSDs for SSD-related operations. Similarly, if there are 10 HDDs in an HDD RAID group and the option raid.min_spare_count is set to 2 at the node level, System Manager leaves 2 HDDs as hot spares and uses the other 8 HDDs for HDD-related operations.

System Manager enforces the hot spare rule for RAID groups when you create an aggregate, edit an aggregate, and when you add HDDs or SSDs to an aggregate. The hot spare rule is also used when you create a storage pool or add disks to an existing storage pool.

There are exceptions to the hot spare rule in System Manager:

  • For MSATA or disks in a multi-disk carrier, the number of hot spares is twice the value set at the node level and the number must not be less than 2 at any time.

  • Hot spares are not used if the disks are part of array LUNs or virtual storage appliances.