Dell PowerVault MD3260 Administrator's Guide - Page 19
RAID Levels, Maximum Physical Disk Support Limitations, RAID Level Usage
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Table 1. RAID Controller Virtual Disk States State Optimal Degraded Offline Force online Description The virtual disk contains physical disks that are online. The virtual disk with a redundant RAID level contains an inaccessible physical disk. The system can still function properly, but performance may be affected and additional disk failures may result in data loss. A virtual disk with one or more member disks in an inaccessible (failed, missing, or offline) state. Data on the virtual disk is no longer accessible. The storage array forces a virtual disk that is in an Offline state to an Optimal state. If all the member physical disks are not available, the storage array forces the virtual disk to a Degraded state. The storage array can force a virtual disk to an Online state only when a sufficient number of physical disks are available to support the virtual disk. RAID Levels RAID levels determine the way in which data is written to physical disks. Different RAID levels provide different levels of accessibility, redundancy, and capacity. Using multiple physical disks has the following advantages over using a single physical disk: • Placing data on multiple physical disks (striping) allows input/output (I/O) operations to occur simultaneously and improve performance. • Storing redundant data on multiple physical disks using mirroring or parity supports reconstruction of lost data if an error occurs, even if that error is the failure of a physical disk. Each RAID level provides different performance and protection. You must select a RAID level based on the type of application, access, fault tolerance, and data you are storing. The storage array supports RAID levels 0, 1, 5, 6, and 10. The maximum and minimum number of physical disks that can be used in a disk group depends on the RAID level: • 120 (180 with premium feature kit) for RAID 0, 1, and 10 • 30 for RAID 5 and 6 Maximum Physical Disk Support Limitations Although PowerVault MD Dense storage arrays with premium feature kit can support up to 180 physical disks, RAID 0 and RAID 10 configurations with more than 120 physical disks are not supported. MD Storage Manager does not enforce 120-physical disk limit when you setup a RAID 0 or RAID 10 configuration. Exceeding the 120-physical disk limit may cause your storage array to be unstable. RAID Level Usage To ensure best performance, you must select an optimal RAID level when you create a system physical disk. The optimal RAID level for your disk array depends on: 19