Dell PowerVault 221S Optimizing Dell SCSI Solutions - Page 35

A REFERENCE GUIDE FOR OPTIMIZING DELL™ SCSI SOLUTIONS VER A02 • Table 5-1: Pros and Cons for Spanning Arrays with various RAID Levels Level RAID 0 RAID 1 RAID 5 RAID 10 RAID 50 Pros Improves data throughput by optimizing bandwidth utilization Improves data availability against channel failures, if mirrored set is spanned across separate channel May improve data throughput for certain accesses, if data and parity for the access span across channels Improves data availability against channel failures, if mirrored set is spanned across separate channel May improve data throughput, similar to spanned RAID5 Cons Reduces reliability and availability of data with additional point of failure - second channel If PV22xS is used on both channels (either in Split of Joined topology), limits the usage of PERC on internal channel (connecting devices to the same channel on internal and external connectors is not supported) Even though RAID5 provides data protection but compromises reliability and availability of data at SCSI channel level If PV22xS is used on both channels (either in Split of Joined topology), limits the usage of PERC on internal channel (connecting devices to the same channel on internal and external connectors is not supported) Reduces reliability and availability of data as compared to non-spanned RAID50 at SCSI channel level Note: Dell PERC controllers don't support spanning of arrays across different controllers. Spanning across channels on the same PERC controller is only supported. Capacity Needs - Virtual Disk Size Virtual disks on SCSI PERC controllers cannot be created with an aggregate size greater than 2TB due to limitations on SCSI controllers and operating systems. Host management application (OMSM, Array Manager) will give an error if an attempt is made to make virtual disk greater than 2TB, prompting user to reduce size of virtual disk. For more information please refer to "Beyond The 2-TB SCSI Logical Unit" white paper at: http://www.dell.com/downloads/global/vectors/2004_2tblun.pdf. Additional RAID information o Dell 'Getting Started with RAID' document http://support.dell.com/support/edocs/storage/RAID/RAIDbk0.pdf PAGE 35 11/17/2005