Data Availability: RAID

Combined RAID Levels

With multiple RAID levels comes increased complexity: many drives are required, and management and maintenance are more complicated.

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RAID 10 - Striping Over Mirror Sets

	RAID 10 combines mirrored drives (RAID 1) with data striping (RAID 0). Data is mirrored, then striped onto another set of drives. This combines the enhanced performance of striping with the added reliability of mirroring. In the walkthrough, notice that a is written to the first disk and then mirrored to the second.
	Then, the next bit of data (b) is striped to the array's third disk and mirrored to the fourth.
	At least four disks are required for RAID 10. Disks must be added two at a time.

	Advantages		Limitations

Better read and write performance than a single disk Good rebuild performance One disk in each mirror set can fail without data loss

A minimum of four disks are required Disks must be added two at a time

RAID 0+1 - Striping of Mirror Sets

	RAID 0+1 combines data striping (RAID 0) with mirrored drives (RAID 1). Data is striped across multiple drives and then written to a mirror set. At least four disks are required for a RAID 0+1. In the walkthrough, bits a, b, and c are striped across the array's first three drives. The stripe is then mirrored to drives four, five, and six.