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Performance Efficient Multiple Logical Unit Number Mapping for Redundant Array of Independent Disks

IP.com Disclosure Number: IPCOM000117769D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Champion, JR: AUTHOR [+4]

Abstract

Disclosed is an algorithm for mapping a Redundant Array of Independent Disks (RAID 5) data space into multiple Small Computer System Interface (SCSI) Logical Unit Numbers (LUNs). This mapping preserves the 1:1 ratio of drive capacity to LUN capacity and is nearly one to one with the component drives in order to provide better seek characteristics.

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Performance Efficient Multiple Logical Unit Number Mapping for Redundant
Array of Independent Disks

      Disclosed is an algorithm for mapping a Redundant Array of
Independent Disks (RAID 5) data space into multiple Small Computer
System Interface (SCSI) Logical Unit Numbers (LUNs).  This mapping
preserves the 1:1 ratio of drive capacity to LUN capacity and is
nearly one to one with the component drives in order to provide
better seek characteristics.

      A RAID 5 storage array is typically one large data space.  Some
operating systems cannot handle such large data spaces.  Therefore,
it is necessary to divide the space into multiple addressable spaces
(LUNs in a  SCSI application).  Another problem with some operating
systems is that  they can not tolerate the size of their configured
data space changing.  This is not unreasonable as individual disk
drives don't suddenly get bigger or smaller.  As a result, adding
drives to an array and keeping  the data accessible to the system is
often difficult or impossible.

      Because RAID 5 uses exactly one drive's capacity for storing
parity data, independent of the number of drives in the array, it is
desirable for a LUN's capacity to be the usable capacity of a drive.
This way, every time a drive is added to the array, an additional LUN
of the same capacity as the previous LUNs is added.  In this case,
the system sees a new LUN that it can configure and use.  Since the
size of the old LUNs hasn't changed, the system doe...