Resultados en tablas y figuras

Note: Theasterisk(*)inIBMtape*representsanumberassignedtoa particular device,suchasIBMtape0.

For tapedrives withattachedmedium changerdevices,theIBMchanger*specialfile provides aseparate pathforissuingcommandstothemediumchanger.Whenthis special fileisopened,theapplication canview themediumchangerasa separate device.Boththetapeand changerspecial filecanbeopenedat thesame time.

Table13.SpecialFilesforIBMUltriumTapeDevices

SpecialFileName RewindonClose

/dev/IBMtape* Yes

/dev/IBMtape*n No

Special Files for the Medium Changer Device

Afterthedriverisinstalledanda mediumchangerdeviceisconfiguredandmade available foruse,accesstotheroboticdeviceisprovidedthrough theIBMchanger special fileinthe/dev directory.Theasterisk(*)representsanumberassignedtoa particulardevice,suchasIBMchanger0.ThetermIBMchangerisusedfora SCSI medium changerdevice.TheIBMchanger*specialfileprovidesa pathforissuing commandstocontrolthemediumchangerroboticdevice.

ThefiledescriptorthatresultsfromopeningtheIBMchangerspecialfiledoesnot support thefollowingoperations:

v Read v Write

v OpeninAppendmode

v Commandsdesignedforatapedevice

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Chapter 28. Alternate Pathing Support for Library Control Path Failover

Note: Thelibrarycontrolpathfailoverfeaturecodemust beinstalledpriorto enablingthealternatepathingsupport intheLinuxIBMtapedevicedriver.

Referto“LibraryControlPathFailoverSupport”onpage12forwhich featurecodeisrequiredforyourmachinetype.

TheLinuxIBMtapedevicedriveralternatepathing supportwillconfiguremultiple physical controlpaths tothesame logicallibrarywithinthedevicedriverand provideautomaticfailovertoan alternatecontrolpathwhena permanenterror occursononepath.Thisistransparenttotherunningapplication.

For example,considera simplemultipathconnectionthatconsistsoftwoHostBus Adapters(HBA)whichareconnected toalibrarywithtwodrivecontrolports enabled.Thefirst HBAisconnectedtothefirst controlportdrive,andthesecond HBAisconnectedtothesecondcontrolportdrive.Thisconnectionprovidestwo physical controlpaths tothesame libraryforredundancyif onepathfromanHBA tothelibraryfails.

Whenthehostbusadapterdevicedrivers areloadedinto therunningsystem,each HBAdetectsa controlporttothesamelibrary,andtwologicaldevicescanbe created (forexample,/dev/IBMchanger0and/dev/IBMchanger1)bythe IBMtapeddaemonortheIBMtapeconfigscript.Eachlogicaldeviceisa physical pathto thesamelibrary.Anapplicationcanopenand useonlyonelogicaldevice at atime, eitherIBMchanger0orIBMchanger1,becausetheyrepresentthesame physical device.WithouttheIBMtapealternatepathing support,ifanapplication opens IBMchanger0andapermanent patherroroccurs(becauseofan HBA,cable, ordrive controlportfailure,forexample),theapplication fails.Itispossibleto initiate manualfailoverbyrestartingtheapplicationonthealternatelogicaldevice (IBMchanger1), butfailingtransactionhastoberestartedfromthebeginning.

Whenthealternatepathingsupportisenabled,thedevicedriverconfiguresthem internally asa singledevicewith multiplepaths.Theapplicationcanstill openand useonlyone logicaldeviceata time(eitherIBMchanger0or IBMchanger1).Ifan application opensIBMchanger0anda permanentpatherroroccurs,thedevice driverinitiatesfailovererrorrecoveryautomaticallyonthealternatepath

(IBMchanger1). Ifsuccessful,thecurrentoperationcontinuesonthealternatepath withoutinterruptingtheapplication.

Configuring and Unconfiguring Alternate Pathing Support

Alternate pathingsupportisnotenabledautomaticallywhenthedevicedriveris installed.TheLinuxIBMtapedevicedriverprovidesadriverparameter

alternate_pathing foryoutoenablethelibrarycontrolpathfailover.

Toenable thefailoversupportin theIBMtapedevicedriversoftware,youneed do thefollowingstepsafterinstallingtheIBMtaperpmpackage:

>IBMtaped stop (stop the IBMtaped daemon)

>rmmod IBMtape (unload the IBMtape driver from the memory) addthefollowinglineinyour /etc/modules.conffile:

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options IBMtape alternate_pathing=1

>depmod

>modprobe IBMtape (re-load the IBMtape driver into memory)

>IBMtaped (re-start IBMtaped daemon)

Youmayignore the″Unresolvedsymbolsin/lib/modules/<yourkernel

name>/drivers/scsi/IBMtape.o″messageafter the″depmod″ command.Youcan check iftheIBMtapedriverhasrecognizedmultiplecontrolpathsforyour library byreadingthe/proc/scsi/IBMchangerfile.

>cat/proc/scsi/IBMchanger

Ifyour librarylists ″Primary″or″Alternate″under″FOPath″,youhave successfullyenabledcontrolpathfailoverfeatureforyour library.Ifit is″NA″

listed under″FOPath″,thenthecontrolpathfailoverisnotenabled.

Afterthealternatepathingsupport isenabled,itremainsset untiltheIBMtape driverisreloadedwith thealternate_pathingdriverparametersettoOFF .The alternatepathing settingisretainedevenif thesystem isrebooted. Ifyouwantto turnoffthecontrolpathfailoverfeatureintheIBMtapedevicedriver,youmaydo thefollowingsteps:

>IBMtaped stop

>rmmod IBMtape

Delete thefollowinglineinyour/etc/modules.conffile:

options IBMtape alternate_pathing=1

>depmod

>modprobe IBMtape

>IBMtaped

Primary and Alternate Paths

WhenIBMtapeisloadedintokernelmemory,thefirstlogicalmediumchanger devicethatIBMtapeseesinthesystemwillbetheprimarypathforthatmedium changer.TheotherlogicalmediumchangersthatIBMtapeattachedforthesame medium changerwillbeconfigured asalternatepaths. Thedevicedriversupports upto 16physical pathsfora singledevice.

The primaryandalternatepathinformationcanbeobtainedbythefollowing command:

>cat /proc/scsi/IBMchanger

The followingisanexampleofa /proc/scsi/IBMchangerfile:

IBMtape version: 1.4.1 IBMtape major number: 253 Attached Changer Devices:

Number Model SN HBA FO Path

0 ULT3583-TL IBM1234567 QLogic Fibre Channel 2200 Primary 1 ULT3583-TL IBM1234567 QLogic Fibre Channel 2300 Alternate 2 ULT3583-TL IBM1234567 QLogic Fibre Channel 2300 Alternate The labelingofalogicaldeviceaseitheraprimaryoralternatepath isfor informationonly,inorderto:

1. Beable toidentifytheactualnumber ofphysicaldevicesconfiguredonthe systemand aspecific logicaldeviceassociatedwith them.Therewillbeonly onelogicaldevicelabeledtheprimary pathforeachphysicaldevice.However, theremaybemultiplelogicaldeviceslabeledasanalternatepathfor thesame devices.

2. Provideinformationaboutwhichlogicaldevices configuredonthesystem have alternatepathing supportenabled.

Querying Primary and Alternate Path Configuration

Youcandisplaytheprimaryandalternatepathconfigurationforalldevices by readingthe/proc/scsi/IBMchangerfile,asexplainedintheabovesection.

Youcanalsodisplaytheprimaryand alternatepathconfigurationforanydevice byrunningthefollowingcommand:

>IBMtapeutil -f /dev/IBMchangerx path

(IBMchangerx is the logical name of any device)

Thiscommandshowsspecificinformationfortheprimarypathandall alternate paths, suchasthelogicalnameofthedevice,theattached hostbusadapter,the channelid,thetarget id,thelogicalunitnumberunderthetarget,thecurrent enabled status,and howmanypathsareconfigured forthedevice.