Lenovo ThinkServer RD240 MegaRAID SAS Software User Guide - Page 64
RAID Availability, 2.7.1 RAID Availability Concept
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RAID Level Capacity 5 RAID 5 provides redundancy for one drive failure without duplicating the contents of entire drives. RAID 5 breaks up data into smaller blocks, calculates parity by performing an exclusive-or on the blocks, then writes the blocks of data and parity to each drive in the drive group. The size of each block is determined by the stripe size parameter, which is set during the creation of the RAID set. 6 RAID 6 provides redundancy for two drive failures without duplicating the contents of entire drives. However, it requires extra capacity because it uses two parity blocks per stripe. This makes RAID 60 more expensive to implement. 00 RAID 00 (striping in a spanned drive group) involves partitioning each drive storage space into stripes that can vary in size. The combined storage space is composed of stripes from each drive. RAID 00 provides maximum storage capacity for a given set of drives. 10 RAID 10 requires twice as many drives as all other RAID levels except RAID 1. RAID 10 works well for medium-sized databases or any environment that requires a higher degree of fault tolerance and moderate to medium capacity. Disk spanning allows multiple drives to function like one big drive. Spanning overcomes lack of disk space and simplifies storage management by combining existing resources or adding relatively inexpensive resources. 50 RAID 50 requires two to four times as many parity drives as RAID 5. This RAID level works best when used with data that requires medium to large capacity. 60 RAID 60 provides redundancy for two drive failures in each RAID set without duplicating the contents of entire drives. However, it requires extra capacity because a RAID 60 virtual drive has to generate two sets of parity data for each write operation. This makes RAID 60 more expensive to implement. 2.7 RAID Availability 2.7.1 RAID Availability Concept Data availability without downtime is essential for many types of data processing and storage systems. Businesses want to avoid the financial costs and customer frustration associated with failed servers. RAID helps you maintain data availability and avoid downtime for the servers that provide that data. RAID offers several features, such as spare drives and rebuilds, that you can use to fix any drive problems, while keeping the servers running and data available. The following subsections describe these features. 2-32 Introduction to RAID
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