File system consistency checking

FSC. or fiOe system FonsLstenFy FKeFk Ls D utLOLty tKDt Ls trDdLtLonDOOy used to Serform D FKeFk on tKe FonsLstenFy of tKe fiOe system; Lf LnFonsLstenFLes Dre found, Lt FDn reSDLr tKem DutomDtLFDOOy or, Ln FertDLn FDses, wLtK tKe KeOS of tKe user. :Lndows users wouOd know Lt by Lts DvDtDr, ‘FKkdsk’.

FLOe systems LnFonsLstenFLes FDn DrLse due to Dn: (D) unFOeDn sKutdown of tKe fiOe system, tySLFDOOy due to either power failure or the user not following proper sKutdown SroFedures; or (b) due to KDrdwDre fDLOures, wKLFK OeDd to tKe fiOe system metD-dDtD LnformDtLon on tKe dLsk beFomLng LnFonsLstent. AOOowLng D ForruSted fiOe system to be used FDn OeDd to furtKer LnFonsLstenFLes Dnd, Ln FertDLn FDses, even to SermDnent dDtD Ooss. HenFe, wKen systems Dre brougKt bDFk onOLne Dfter D FrDsK, oSerDtors KDve been known to run tKe ‘fsFk’ before tKe fiOe system FDn be mDde onOLne Dnd user IO oSerDtLons DOOowed on Lt.

FSC. LndeSendentOy trLes to buLOd Lts knowOedge of tKe struFture Dnd ODyout of tKe fiOe system from tKe vDrLous dDtD struFtures on dLsk, Dnd ForroborDtes Lt wLtK tKe summDry/FomSuted LnformDtLon mDLntDLned by tKe fiOe system. If tKe two SLeFes of LnformDtLon don’t mDtFK, Dn LnFonsLstenFy Ls deteFted Dnd FSC. trLes to reSDLr tKe LnFonsLstenFy. If DutomDtLF reSDLr Ls not SossLbOe, tKe problem is reported to the user. A good overview of cSCK can be found in http://lwn.net/Articles/248180/.

Here Ls D TuestLon to our reDders. Do DOO fLOe systems need D FSC. utLOLty? For LnstDnFe, tKere Dre fLOe systems tKDt suSSort MournDOLng or wrLte-DKeDd OoggLng, wherein all changes to metadata are first logged on to D MournDO Oog on SersLstent medLD before tKe metDdDtD LtseOf Ls uSdDted. FLOe system LnFonsLstenFLes FreDted by partial metaJdata writes resulting from a sudden crash wKLOe oSerDtLons Dre Ln mLd-fOLgKt Dre Dddressed by meDns of tKe fLOe system MournDO Oog, wKLFK FDn reSODy the log on restart and recover to a consistent state. Do suFK MournDOLng fLOe systems need FSC.?