Disks provide the basic unit of storage for storage systems running Data ONTAP that use native disk shelves. Understanding how Data ONTAP uses and classifies disks will help you manage your storage more effectively.
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How Data ONTAP reports drive types
Data ONTAP associates a type with every drive. Data ONTAP reports some drive types differently than the industry standards; you should understand how Data ONTAP drive types map to industry standards to avoid confusion.
Storage connection architectures and topologies supported by Data ONTAP
Data ONTAP supports two storage connection architectures: serial-attached SCSI (SAS) and Fibre Channel (FC). The FC connection architecture supports three topologies: arbitrated loop, switched, and point-to-point.
Usable and physical disk capacity by disk size You cannot use the nominal size of a disk in your aggregate and storage system capacity calculations. You must use either the usable capacity or the physical capacity as calculated by Data ONTAP.
Methods of calculating aggregate and system capacity
You use the physical and usable capacity of the disks you employ in your storage systems to ensure that your storage architecture conforms to the overall system capacity limits and the size limits of your aggregates.
Disk speeds supported by Data ONTAP
For hard disk drives, which use rotating media, speed is measured in revolutions per minute (RPM). Faster disks provide more disk input/output operations per second (IOPS) and faster response time.
How disk checksum types affect aggregate and spare management
There are two checksum types available for disks used by Data ONTAP: BCS (block) and AZCS (zoned). Understanding how the checksum types differ and how they impact storage management enables you to manage your storage more effectively.
Checksum type by Data ONTAP disk type
You should know the Data ONTAP disk type and checksum type of all of the disks you manage, because these disk characteristics impact where and when the disks can be used.
Drive name formats
Each drive has a name that differentiates it from all other drives. Drive names have different formats, depending on the connection type (FC-AL or SAS) and how the drive is attached.
Understanding 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; it is different from the Data ONTAP disk type.
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 sanitization process to ensure that no one can recover the data on the disks.
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.
Increasing storage availability by using ACP
ACP, or Alternate Control Path, is a protocol that enables Data ONTAP to manage and control a SAS disk shelf storage subsystem. It uses a separate network (alternate path) from the data path, so management communication is not dependent on the data path being intact and available.
How you use SSDs to increase storage performance
Solid-state disks (SSDs) are flash memory-based storage devices that provide better overall performance than hard disk drives (HDDs), which are mechanical devices using rotating media. You should understand how Data ONTAP manages SSDs and the capability differences between SSDs and HDDs.
Guidelines and requirements for using multi-disk carrier disk shelves
Data ONTAP automatically handles most of the extra steps required to manage disks in multi-disk carriers. However, there are some extra management and configuration requirements that you must understand before incorporating multi-disk carrier disk shelves in your storage architecture.
Adding disks to a storage system
You add disks to a storage system to increase the number of hot spares, to add space to an aggregate, or to replace disks.
Replacing disks that are currently being used in an aggregate
You can use the disk replace command to replace disks that are part of an aggregate without disrupting data service. You do this to swap out mismatched disks from a RAID group. Keeping your RAID groups homogeneous helps optimize storage system performance.
Replacing a self-encrypting disk
Replacing a self-encrypting disk (SED) is similar to replacing a regular disk, except that there are some extra steps you must take to reenable Storage Encryption after you replace the disk.
Removing disks from a storage system
How you remove a disk from your storage system depends how the disk is being used. By using the correct procedure, you can prevent unwanted AutoSupport notifications from being generated and ensure that the disk will function correctly if it is reused in another storage system.
