| Monday May 30th 2016

RAID Write Back vs Write Through

RAID hard drive arrayTo suffer or not to suffer?  That is the question.

RAID Features

Write Through Cache
With Write Through Cache the data is written to both the cache and drive once the data is retrieved. As the data is written to both places, should the information be required it can be retrieved from the cache for faster access. The downside of this method is that the time to carry out a Write operation is greater the time to do a Write to a non cache device. The total Write time is the time to write to the cache plus the time to Write the disk.

Write Back Cache
With Write Back Cache the write operation does not suffer from the Write time delay. The block of data is initially written to the cache, only when the cache is full or required is the data written to the disk.

The limitation of this method is that the storage device for a period of time does not contain the new or updated block of data. If the data in the cache is lost due to power failure the data cannot be recovered. When using Write Back Cache a battery backup module would prevent data loss in a RAID power failure.


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