Disk Spin-down
Definition
The disk spin-down is to set the disks that have not undertaken write/read operations for a long time to spin down. The drive motor and the magnetic head of a spin-down disk stop running. The disk spins up when new I/O requests are delivered.
Purposes
The purposes of the disk spin-down is to lower the consumption of the storage system without effecting the write/read performance of the system and improve the energy efficiency of the storage system.
Benefits
The disk spin-down greatly reduces the power consumption, lowers the operating cost, and shortens the operating time of free disks, which prolongs disks' service life.
Availability
You do not need to purchase an extra license for disk spin-down.
Principles
The disk spin-down technology of the N8500 is in the units of RAID groups. After confirming that the data in the RAID group is the near-line or offline data, you can set the RAID group to allow its hard disks to spin or wake up. All the hard disks in a RAID group can be spun down or up as required; however, the disk spin-down technology does not apply for a single hard disk.
- If no I/O is accessed in the RAID group, all the hard disks in the RAID group are spun down, that is, all the hard disks stop rotating.
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If I/O is still accessed to any hard disk in the RAID group, the RAID group cannot be spun down.
After a RAID group is spun down, to read data from or write data to any of its hard disk, the RAID group needs to be spun up first. You can spin up a spun-down RAID group through either of the following methods:
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Automatic I/O spin-up
For a spun-down RAID group, if new I/O applications are sent to any hard disk in the RAID group, the applications queue for the storage system to spin up all the hard disks in the RAID group, and after that, the applications can be sent. There is a restart latency of 10 to 15 seconds during the hard disk is changed from spun down to running.
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Control command spin-up
As the automatic I/O spin-up method delays new I/O processing for 10 to 15 seconds, it is not suitable for applications that allow little latency. For latency-sensitive applications, use control commands to immediately spin up the RAID group.
Application Scenarios
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Backup and Archiving Applications
When N8500mainly stores backup data when it serves as a backup array. Generally, backup data is seldom accessed; for example, non-hot data on the backup array might not be accessed for up to a year. The disks storing such data can be set to spin down and then to spin up when data access is requested. This mechanism reduces power consumption and greatly prolongs the service life of backup disks.
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Streaming Media and Video Surveillance Applications
When N8500 is used for video-on-demand (VoD) data storage applications, VoD files that are seldom accessed can be stored in the RAID group that is set to spin down. Hot files are stored in another RAID group for a quicker response.
For video surveillance applications, monitoring data can be deleted only when it is stored for a certain period and outdated data can be kept as required. If outdated data is seldom accessed, the related RAID group can be set to spin down to save power and protect the disks.
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Special Industries and Scenarios
For example, the storage unit can be used in the health sector's picture archiving and communication systems (PACS). PACS mainly stores high volumes of medical images and videos of operations. Data is saved in the storage system for archiving and recording purposes, case studies and statistics, follow-up consultations, and appraisals. Laws and regulations require the long-term storage of medical data, though this data is seldom accessed. Disk spin-down function greatly reduces power consumption and ensures rapid data access if needed.
