Variable stripe RAID support using virtual LUNs (19-Jan-2010)

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IP.com Prior Art Database Disclosure (Source: IPCOM)

Disclosure Number IPCOM000191964D dated 19-Jan-2010

Originally published in Prior Art Database

Disclosed by: Unspecified

Country: United Kingdom

Related People

Howard Winter - INVENTOR

Disclosure File: 4 pages / 115.0 KB / English (United Kingdom)

Enabling a RAID controller to support a mixture of stripe sizes and configurations over the same array simultaneously and dynamically, thereby allowing stripe sizes to be optimised for different data types and access patterns.

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Variable stripe RAID support using virtual LUNs

Introduction

Existing RAID controllers, once configured, normally have a fixed stripe size and configuration (raid 0, 1, 5 or 6 etc) over the entire array (or sub-arrays).

This invention allows a RAID controller to support a mixture of stripe sizes and configurations over the same array simultaneously and dynamically.

Optimal stripe size may vary for different data types and access patterns; one size does not necessarily fit all.

Some file systems use variable-sized stripes to improve performance, reliability and avoid read-modify-write. These are not currently supported by hardware RAID controllers.

One stripe configuration may not be appropriate for all data types, i.e. mixtures of critical and non-critical data. Therefore the ability to support a mixture of stripe sizes and configurations is useful.

Description of the invention

· The array is presented as a number of virtual LUNs.

· Each virtual LUN represents a different way of accessing the same array of disks.

· Each virtual LUN represents a different stripe size and configuration.

· The LUN number is used to direct the operation of the RAID controller, otherwise it functions as a ‘dumb’ block device.

· It assumes the stripe is formed of contiguous reads or writes in the configuration determined by the LUN number.

· The user is responsible for policing of non-compatible or overlapping stripes.

· Rebuild is driven by reads – it may be possible to use spare space (520/528B blocks) to tag a stripe configuration for auto-rebuild.

Consider an existing RAID array with the following configuration:-

· 8 data drives and 1 parity drive.

· Drive block size of 512 bytes, stripe size of 8 KB = 16 blocks.

LBA	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5	Disk 6	Disk 7	Disk 8	Disk 9
0	D₀	D₂	D₄	D₆	D₈	D₁₀	D₁₂	D₁₄	P₀
1	D₁	D₃	D₅	D₇	D₉	D₁₁	D₁₃	P₁	D₁₅
2	D₀	D₂	D₄	D₆	D₈	D₁₀	P₀	D₁₂	D₁₄
3	D₁	D₃	D₅	D₇	D₉	P₁	D₁₁	D₁₃	D₁₅

N

By way of example consider a RAID controller with a number of virtual LUNs. The same array of disks can be represented in many ways:

Virtual LUN	Configuration
0	Raw 512B
1	512B + mirror
2	1KB stripe + parity
3	2KB stripe + parity
4	4KB stripe + parity
5,6,7,8	8,16,32,64KB stripe + parity
9	128KB stripe + parity

Obviously many more options exist, including raid 6, non-modulo 2 sizes and alternative alignments.

Virtual LUN 0, RAW 512B:

LBA	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5	Disk 6	Disk 7	Disk 8	Disk 9
N		D₀	D₀				…	…	…
N+1					D₀	D₀		D₀

Virtual LUN 1, 512B + mirror:

LBA	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5	Disk 6	Disk 7	Disk 8	Disk 9
N			D₀	M₀	D₁	M₀			..
N+1		D₂	M₂

Virtual LUN 3, 2KB + parity:

LBA	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5	Disk 6	Disk 7	Disk 8	Disk 9
N	D₀	D₁	D₂	D₃	P₀
N+1							D₀	D₁	D₂
N+2	D₃	P₀						D₀	D₁
N+3	D₂	D₃	P₀

Virtual LUN 5, 8KB + parity:

LBA	Disk 1	Disk 2	Disk 3	Disk 4	Disk 5	Disk 6	Disk 7	Disk 8	Disk 9
N	D...

(Source: IPCOM)

(Source: IPCOM)

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