Backup and Recovery Strategies.docx

Backup and Recovery Strategies.docx

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BackupandRecoveryStrategies

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BackupandRecoveryStrategies

Thischapteroffersguidelinesandconsiderationsfordevelopinganeffectivebackupandrecoverystrategy.

Thissectionincludesthefollowingtopics:

∙DataRecoveryStrategyDeterminesBackupStrategy

∙PlanningDataRecoveryStrategy

∙PlanningBackupStrategy

∙ValidatingYourDataRecoveryStrategy

DataRecoveryStrategyDeterminesBackupStrategy

Todecideonbackupstrategies,startwithyourdatarecoveryrequirementsandyourdatarecoverystrategy.Eachtypeofdatarecoverywillrequirethatyoutakecertaintypesofbackup.

Failurescanrunthegamutfromusererror,datafileblockcorruptionandmediafailuretosituationslikethecompletelossofadatacenter.Howquicklyyoucanresumenormaloperationofyourdatabaseisafunctionofwhatkindsofrestoreandrecoverytechniquesyouincludeinyourplanning.Eachrestoreandrecoverytechniquewillimposerequirementsonyourbackupstrategy,includingwhichfeaturesoftheOracledatabaseyouusetotake,storeandmanageyourbackups.

Whenthinkingaboutrecoverystrategies,askyourselfquestionslikethese:

∙Ifadiskfailedanddestroyedsomeofthedatabasefiles,suchasdatafilesorredologs,howwouldyourecoverthelostfiles?

Asdescribedin"PlanningaResponsetoMediaFailure:

RestoreandMediaRecovery",youshouldbeabletohandlethelossofdatafiles,controlfiles,andonlineredologs.

∙Ifalogicerrorinanapplicationorausererrorcausedthelossofimportantdatafromoneorseveraltablesortablespaces,howcouldyourecoverthatdata,andwhatwouldhappentodatabaseupdatessincetheerror?

Couldyoudeterminethecauseoftheerror,topreventitfromhappeningagain?

Asdescribedin"PlanningaResponsetoUserError:

Point-in-TimeRecoveryandFlashbackFeatures",techniquesavailabletoyouincludepoint-in-timerecoveryofthewholedatabaseoroneormoretablespaces,importingdatafromearlierlogicalexportswithoneofthedataimportutilities,andusingtheOracledatabase'sflashbackfeatures.

∙Iftheinstancealertlogindicatesthatoneormoretablescontainscorruptblocks,howcanyourepairthecorruption?

Doesthetablespacehavetoremainavailableduringtherepair?

Asdescribedin"PlanningaResponsetoDatafileBlockCorruption:

BlockMediaRecovery",theRMANBLOCKRECOVERcommandcanhelpyouinthissituation.Also,troubleshootrecoverywiththeSQL*PlusRECOVER...TESTcommand.

∙Iftheentiredatacenterisdestroyed,canyouperformdisasterrecovery?

Assumethatallyouhaveisanarchivetapecontainingbackups.Howwouldyourecoverthedatabase?

Howlongwouldthatrecoverytake?

∙Ifyouwerenotavailabletorecoveryourdatabase,couldsomeoneelserecoveritinyourabsence?

Areyourrecoveryproceduressufficientlyautomatedanddocumented?

Withtheseneedsinmind,decidehowyoucantakeadvantageoffeaturesrelatedtobackupandrecovery,andlookathoweachfeaturemeetssomerequirementofyourbackupstrategy.Forexample:

∙UsingRecoveryManagersimplifiesmostbackupandrecoveryoperationscomparedtouser-managedbackupandrecovery.Itautomatesmanagementofmostbackupfiles,includingthedeletionofbackupsandarchivedredologsfromdiskortapewhennolongerneededtomeetrecoverygoals.Itprovidesdetailedreportingonbackupactivities,canverifythatyouravailablebackupscanbeusedtorecoveryourdatabase.Finally,RMANmakespossiblemanyrecoverytechniquesnotavailableifyouareusinguser-managedbackupandrecovery,suchasincrementalbackups.

∙FlashbackDatabasewillhelpyourestoreadatabasetoaprevioustimemuchfasterthanmediarecovery.However,youmustdecideinadvancetokeepflashbacklogs,andkeepingflashbacklogsrequiresthatyouconfigureaflashrecoveryarea.

∙Blockmediarecoverymaybebetterthandatafilemediarecoveryifavailabilityiscritical.WhileblockmediarecoveryispossibleevenifyoudonotbaseyourbackupandrecoverystrategyonRMAN,RMAN-basedblockmediarecoverycanbeperformedmorequicklyandwithlesseffort.

Onceyoudecidewhichfeaturestouseinyourrecoverystrategy,youcanplanyourbackupstrategy,answeringthefollowingquestions,amongothers:

∙Howandwherewillyoustoreyourrecovery-relatedfiles?

Willyouuseaflashrecoveryarea?

WillyouuseanASMdiskgroup?

Willyoustorebackupsontapeorotherofflinestorage,oronlyondisk?

∙Atwhatintervalswillyoutakescheduledbackups?

Andwhatformofphysicalbackupswillyoutakeineachsituation?

∙Whatsituationsrequireyoutotakeadatabasebackupoutsideoftheregularschedule?

Sometimesyoumusttakeanunscheduledbackuptoensurethatyoucanrecoveryourdata,suchasafteranOPENRESETLOGSorafterchangestoyourdatabasesuchasNOLOGGINGoperationsthatdonotappearintheredolog.Youmayalsohavebusinessrequirementsthatrequirebackupsforauditingpurposesorotherreasonsnotrelatedtodatabaserecovery.

∙Howcanyouvalidateyourbackups,toensurethatyoucanrecoveryourdatabasewhennecessary?

∙Howdoyoumanagerecordsofyourbackups?

∙Doyouhavedetailedrecoveryplansthatcovereachtypeoffailure?

HowdoyourDBAscanexecutetheseplansinacrisis?

Canscriptsbewrittentoautomateexecutionoftheseplansinacrisis?

∙CanyouapplyOracledatabaseavailabilitytechnologies,suchasDataGuardorRealApplicationClusters,toimproveavailabilityduringadatabasefailure?

Howdoesusingtheseavailabilitytechnologiesaffectyourbackupandrecoverystrategy?

Theseareofcourseonlyafewoftheconsiderationsyoushouldtakeintoaccount.Availableresources（hardware,media,staff,budget,andsoon）willalsobefactorsinyourdecision.

PlanningDataRecoveryStrategy

Yourdatarecoverystrategyshouldincluderesponsestoanynumberofdatabasefailurescenarios.Thekeytoaneffective,efficientstrategyisenvisioningfailuremodes,matchingOracledatabaserecoverytechniquesandtoolstothefailuremodesinwhichtheyareuseful,andthenmakingsureyouincorporatethenecessarybackuptypestosupportthoserecoverytechniques.

Tohelpmatchfailuremodestorecoverytechniquesthatcanhelpresolvethem,refertothefollowingsections:

∙PlanningaResponsetoUserError:

Point-in-TimeRecoveryandFlashbackFeatures

∙PlanningaResponsetoMediaFailure:

RestoreandMediaRecovery

∙PlanningaResponsetoDatafileBlockCorruption:

BlockMediaRecovery

PlanningaResponsetoUserError:

Point-in-TimeRecoveryandFlashbackFeatures

Yourbackupandrecoverystrategyshouldenableyoutohandlesituationsinwhichauserorapplicationmakesunwantedchangestodatabasedata,suchasdeletingthecontentsofatableormakingincorrectupdatesduringabatchrun.Thegoalinsuchacasewillbetorestoretheaffectedpartsofyourdatabasetotheirstatebeforetheusererror.

Dependingonthesituation,yourappropriateresponsewillbeoneofthefollowing:

∙Ifyouhaveperformedalogicalbackupbyexportingthecontentsoftheaffectedtables,sometimesyoucanimportthedatabackintothetable.Thistechniquepresumesthatyouareregularlyexportinglogicalbackupsofyourdata,andthatanychangesbetweenexportsareunimportant.

∙Youcanperformpoint-in-timerecovery,bringingonetablespaceorthewholedatabasebacktoitsstatebeforethetimeoftheerror.Ineithercase,youneedbackupsfrombeforethetimeoftheerror,plustheredologsfromthetimeofthebackuptothetimeoftheerror.

Note:

Oracle'sFlashbackTechnologyprovidesfasterandlessdisruptivealternativestomediarecoveryinmanycircumstances.

∙OracleFlashbackDatabaseisaphysical-levelrecoverymechanismsimilartomediarecovery,butgenerallyfasterandnotrequiringtherestoreofdatafrombackup.

∙OracleFlashbackTableandOracleFlashbackDropworkatthelogicallevel,undoingunwantedchangestotables,includingreversingtheeffectsofDROPTABLEstatements.

∙OracleFlashbackQueryandOracleFlashbackVersionQueryareusefulinviewingpastcontentsoftablesandinvestigatinghowandwhenlogicalcorruptionsaffectedyourdatabase.

InformationaboutthesefeaturesiscollectedinOracleDatabaseBackupandRecoveryAdvancedUser'sGuide.Thisdocumentwillalludetosuchfeatureswheretheycanbehelpfulandprovidepointersformoreinformation.Familiarizeyourselfwiththesefeaturesbeforeplanningyourbackupandrecoverystrategy,becauseyoumayfindthattheycanbequitevaluableandrequirelimitedadvancedplanning.

PlanningaResponsetoMediaFailure:

RestoreandMediaRecovery

AmediafailureoccurswhenaproblemexternaltothedatabasepreventsOraclefromreadingfromorwritingtoafileduringdatabaseoperations.Typicalmediafailuresincludephysicalfailures,suchasheadcrashes,andtheoverwriting,deletionorcorruptionofadatabasefile.Mediafailuresarelesscommonthanuserorapplicationerrors,butyourbackupandrecoverystrategyshouldprepareforthem.

Thetypeofmediafailuredeterminestherecoverytechniquetouse.Forexample,thestrategyyouusetorecoverfromacorrupteddatafileisdifferentfromthestrategyforrecoveringfromthelossofthecontrolfile.

Example:

OnlineRedoLogRecovery

Themethodofrecoveryfromlossofallmembersofanonlineloggroupdependsonanumberoffactors,suchas:

∙Thestateofthedatabase（open,crashed,closedconsistently,andsoon）

∙Whetherthelostredologgroupwascurrent

∙Whetherthelostredologgroupwasarchived

Forexample:

∙Ifyoulosethecurrentgroup,andthedatabaseisnotclosedconsistently（eitheritisopen,orithascrashed）,thenyouwillhavetorestore