Tuesday, October 6, 2009

RAID and Oracle - Performance Issues

The various RAID configurations are all appropriate if used correctly, and no RAID configuration is 'best' for all situations.
· use where availability is essential AND write performance requirements eliminates RAID 5
· doubles cost of storage (2x2Gb disk = 2Gb storage)
· costs 5-15% in performance is using SW RAID (e.g. NT)
· use where availability is important, AND 'read' will be the majority of I/O's
· costs about 20% (5 member stripe) to 33% (3 member stripe)
· decreases WRITE performance by 1/4 (5 members) to 1/3 (3)
· increases READ (for larger reads) by 1.5 to 3x (usually limited by xfer capacity of SCSI channel)
· a single failure will crash entire stripe set
· 100% storage efficiency
· READ and WRITE performance can be much higher (depending upon geom. of stripe set)
NOTE: THIS ASSUMES SOFTWARE RAID ONLY - there are some VERY GOOD implementations of RAID with caching, separate RISC cpu's etc These have to be evaluated independently due to the various algor. they can use.
These are also more expensive (redundant everything ...) but can really make your day when needed !

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