HP AiO400t HP StorageWorks All-in-One Storage System User Guide (440583-006, J - Page 80
Setting a percent full warning threshold, Description, RAID level
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RAID level Description RAID 1+0 - Mirroring and Striping Offers the best combination of data protection and performance. RAID 1+0 or drive mirroring creates fault tolerance by storing duplicate sets of data on a minimum of four hard drives. There must be an even number of drives for RAID 1+0. RAID 1+0(10) and RAID 1 are the most costly fault tolerance methods because they require 50 percent of the drive capacity to store the redundant data. RAID 1+0(10) first mirrors each drive in the array to another, and then stripes the data across the mirrored pair. If a physical drive fails, the mirror drive provides a backup copy of the files and normal system operations are not interrupted. RAID 1+0(10) can withstand multiple simultaneous drive failures, as long as the failed drives are not mirrored to each other. RAID 5 - Distributed Data Guarding Offers the best combination of data protection and usable capacity while also improving performance over RAID 6. RAID 5 stores parity data across all the physical drives in the array and allows more simultaneous read operations and higher performance than data guarding. If a drive fails, the controller uses the parity data and the data on the remaining drives to reconstruct data from the failed drive. The system continues operating with a slightly reduced performance until you replace the failed drive. RAID 5 can only withstand the loss of one drive without total array failure. It requires an array with a minimum of three physical drives. Usable capacity is N-1 where N is the number of physical drives in the logical array. RAID 6- Advanced Data Guarding (ADG) Offers the best data protection and is an extension of RAID 5. RAID 6 uses multiple parity sets to store data and can therefore tolerate up to 2 drive failures simultaneously. RAID 6 requires a minimum of 4 drives and is available only if the controller has an enabler. Writer performance is lower than RAID 5 due to parity data updating on multiple drives. It uses two disk for parity; its fault tolerance allows two disks to fail simultaneously. Usable capacity is N-2 where N is the number of physical drives in the logical array. Setting a percent full warning threshold To receive a warning alert when storage capacity reaches a specified limit, set the percent full warning threshold. You can set a warning threshold for any application component, user-defined application, and shared folder that ASM manages. An iSCSI LUN application will not have a warning threshold. By default, the warning threshold is set to 80%. To change it, enter a new percent value on the Advanced window. After you set a warning threshold, ASM changes the status indicator for the application component, user-defined application, or shared folder when this threshold has been surpassed. This is a warning only; no hard limits are enforced on storage capacity as a result of setting this value. The warning is visible in these places: • A yellow warning icon appears on the application component, user-defined application, or shared folder icon in the content pane. • As an alert in the Properties window. 80 Hosting storage for applications and shared folders