Disks provide the basic unit of storage for storage systems running Data ONTAP. Understanding how Data ONTAP uses and classifies disks will help you manage your storage more effectively.
What disk types Data ONTAP supports
Data ONTAP supports four disk types: Fibre Channel (FC), Advanced Technology Attachment (ATA), Serial Advanced Technology Attachment (SATA), and Serial Attached SCSI (SAS).
Disk connection architectures
Data ONTAP supports two disk connection architectures: Fibre Channel Arbitrated Loop (FC-AL) and Serial Attached SCSI (SAS).
Available disk capacity by disk size
To maintain compatibility across brands of disks, Data ONTAP rounds down ("right-sizes") the amount of space available for user data.
Disk speeds
Disk speeds are measured in revolutions per minute or RPM. It is best to use disks of the same speed in an aggregate. Faster disks provide more disk input/output operations per second (IOPS) and faster response time.
Disk formats
The disk format determines how much of the disk’s raw capacity can be used for data storage. Also, some disk formats cannot be combined in the same aggregate.
Disk names
Each disk has a unique name that differentiates it from all other disks in the storage system. Disk names have different formats depending on the disk connection type (FC or SAS) and whether the disk is directly attached to the storage system or attached to a switch.
RAID disk types
Data ONTAP classifies disks as one of four types for RAID: data, hot spare, parity or dparity. The RAID disk type is determined by how RAID is using a disk.
Disk pools
Data ONTAP uses four disk pools to track disk drive states: the spares pool, the maintenance pool, the broken pool, and the pool of disks that are currently in use in an aggregate. To see all disks in all pools, you can use the aggr status -r command
How disk sanitization works
Disk sanitization is the process of physically obliterating data by overwriting disks with specified byte patterns or random data so that recovery of the original data becomes impossible. You use the disk sanitize command if you want to ensure that no one can recover the data on the disks.
Commands to display disk information
You can see information about your disks using several commands, including the aggr, disk, fcstat, sasadmin, storage, sysconfig and sysstat commands.
How Data ONTAP monitors disk performance and health
Data ONTAP continually monitors disks to assess their performance and health. When Data ONTAP encounters certain errors or behaviors from a disk, it takes the disk offline temporarily or takes the disk out of service to run further tests.
