Oracle ASM and Multi-Pathing Technologies
Doc ID: Note:294869.1
This document will briefly discuss Multipath I/O and how Oracle Automatic Storage Management leverages multi-pathing.
An I/O path generally consists of an initiator port, fabric port, target port, and LUN. Each permutation of this I/O path is considered an independent path. Dynamic Multi-pathing/failover tools aggregate these independent paths into a single logical path. This path virtualization provides I/O load-balancing across the HBAs, as well as non-disruptive failover on HBA failures. Multi-pathing software requires all the required disks to be visible on each available and eligible HBA. These multi-paths will be detected by probing the World Wide Device Identifiers (WWD ID).
Multi-pathing software also provides multi-path software drivers. Most multi-pathing drivers are SCSA compliant pseudo nexus drivers, that support multipath services for fibre channel attached SCSI-3 devices. These drivers receive naming and transport services from one or more physical HBA devices. To support multi-pathing, a physical HBA driver must comply with the multi-pathing services provided by this driver.
Multipaths provides the following benefits:
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Provide a single block device interface for a multi-pathed LUN
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Detect any component failures in the I/O path; e.g., fabric port, channel adapter, or HBA.
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When a loss of path occurs, ensure that I/Os are re-routed to the available paths, with no process disruption.
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Reconfigure the multipaths automatically when events occur.
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Ensure that failed paths get revalidated as soon as possible.
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Provide auto-failback capabilities.
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Configure the multipaths to maximize performance using various load balancing methods; e.g., round-robin, least I/Os queued, or least service time.
Examples of multi-pathing software include EMC PowerPath, Sun Traffic Manager and IBM MPIO.
Although most of these tools are storage array agnostic, some require additional software components and drivers specific for the storage
Note, Oracle Corporation does not certify or qualify these tools. Oracle10g includes a new feature called Automatic Storage Management (ASM). ASM provides filesystem and volume manager capabilities built into the Oracle database kernel. With this capability, ASM simplifies storage management tasks, such as creating/laying out databases and disk management. Although ASM does not provide multi-pathing capabilities, ASM does leverage multi-pathing tools, as long the path or device produces a successful return code from an fstat system call.
The table below describes the attributes of the utilities and how it can be used by ASM.
Multi-pathing tool
ASM Device Usage
Notes
1）AIX 系统
多路径软件EMC PowerPath
Use raw partitions thru
As of this writing, SDD-AIX is known to cause discovery and device handling problems for ASM, and thus is not viable solution.
See SDDPCM section below for an alternative solution to SDD for AIX
Use /dev/rhdiskx device
You m ust install SDDPCM filesets and enable SDDPCM.. SDDPCM cannot co-exist w/ SDD.
Use /dev/rdsk/cxtydz that’s generated by HDLM
HDLM generates a scsi (cxtydzx) address where the controller is highest unused controller number.
Use /dev/rhdisk device
2）HP 系统
多路径软件EMC PowerPath
ASM can use the raw partitions. Must use native device path:
ASM can use the raw partitions.
Use /dev/rdsk/cHtydz that’s generated by HDLM
HDLM generates a scsi address like cHtydz.
ASM can use the pseudo device.
The pseudo device will have the Global Unique Identifier included its name.
3）Sun 系统
多路径软件PowerPath
ASM will use raw partitions, associated with the pseudo device:
多路径软件Sun Traffic Manager
ASM can use the pseudo device.
The pseudo device will have the Global Unique Identifier included its name.
Use /dev/rdsk/cxtydz that’s generated by HDLM
HDLM generates a scsi (cxtydzx) address where the controller is highest unused controller number.
Use /dev/FJSVmplb/[r]dsk/mplbI*1s{0-7}. *1 "I" is MPLB Instance number
4）Linux 系统
多路径软件IBM-SDD
ASM can use the raw device associated with the Vpath.
You must use SDD-Linux driver 1.6.05+ . Goto IBM SDD site to get latest driver
DS6000
Enterprise Storage Server (ESS)
SAN Volume Controller (SVC)
ASM can use raw partitions associated with the /dev/emcpowerx device.
Associate the raw devices with the PP device.
ASM should use raw devices associated with /dev/spx
Currently SecurePath is only available on x86 and Itanium, all other 64bit platforms are not supported
ASM can use raw device associated with /dev/mdx device.
Though not a real multipath solution, it does provide rudimentary active/passive support
ASM can use the name generated by DM:
Avail in 2.6 kernel. Refer to following note for specifics
Use /dev/rdsk/cxtydz that’s generated by HDLM
HDLM generates a scsi (cxtydzx) address where the controller is highest unused controller number.
Associate raw device to /dev/FJSVmplb/[r]dsk/mplbI*1s{0-7}