sees VLeZBo nteJratLnJ LocaO FLOe Sstems Yupu KanJx000f CKrLs DraJJax000f Andrea ArpacLDusseaux000f RemzL ArpacLD Incredibly popular Dropbox has 100 million usersBack up files to th ID: 824692
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cloud state file system stateLocal file
cloud state file system stateLocal file system is the weakest linkCorruption and inconsistency are exposedAd-hoc synchronization is harmfulSync client sees what regular application sees, but not what file system seesVLeZBo[: ,nteJratLnJ LocaO FLOe S\stems Yupu =KanJ CKrLs DraJJa Andrea ArpacL-Dusseau RemzL ArpacL-DIncredibly popular: Dropbox has 100 million+ usersBack up files to the cloudSynchronize files across multiple clients,s Your Data ReaOO\ Safe?VLeZBo[ArcKLtectureMany copies do NOT always make your data safeOur SoOutLon -VLeZBo[Local detection + Cloud-aided recoveryclient sees what file system seesBuilt around ext4 and two services: Dropbox and SeafileLess than 5% overhead for most workloadsUp to 30% reduction of sync time in some casesVLeZ ManaJerPre-allocated checksum region (~0.1% overhead)Each checksum maps to a data block32-bit CRC checksum per 4KB blockDetect data corruption & inconsistencyLocal detection (ext4-cksum)Detect corruption & inconsistency using cksumInitiate recoveryLocal FS is dedicated to the entire sync folderCloud-aided recovery (Cloud Helper)Recover from corruption and crashes using synchronized views on cloudView-based synchronization (View Manager)Basis for consistency and correct recoveryPresent file systems view to sync serviceOther applications view remains the sameThree types of viewsActive view (local)=�current FS stateFrozen view (loc�al) =last snapshot in memorySynced views �(on cloud) = uploaded viewsUser-level daemonTalk to local FS through ioctlCommunicate with cloud through web APIRecover from corruptionFetch correct block from cloudRecover from crashRecover inconsistent filesRollback FS to latest synced view on cloudHuge increase in sync time ViewBoxand Dropbox, due to Dropboxs lacking of view-APIViewBoxand Seafileimprove sync due to reduced interference from foreground updatesfile system state correct statecloud state file system stateintegratedfile system and cloud storagefile system state correct stateFSs viewCloud Sync ClientViewApplicationSynced ViewsFrozen ViewActive ViewFS Epoch4Tech #1 -Cloud Journaling Synced ViewsFrozen ViewActive ViewFS Epoch4Synced ViewsFrozen ViewActive ViewFS Epoch41E2changed filenamespacechanged filenamespaceTech #2 -Incremental Snapshottingchanged filenamespaceSynced ViewsFrozen ViewActive ViewFS Epoch4Create frozen views at FS epochs Upload frozen views to cloudStore multiple views on cloud for recovery Treat cloud storage as external journalDecouple namespace and dataLog namespace changes and data changes Apply namespace changes to last frozen viewData is left in FS, but marked COWRe-generate inotifyevents4DropboxSeafileSync time (sec)ext4ViewBox0DropboxSeafileRuntime (sec)ext4ViewBox01000200025003000DropboxSeafileSync time (sec)ext4ViewBoxViewBoxdoes not affect foreground workloadRuntime overhead Photo ViewingPhoto ViewingPhoto EditingRe%00;liability = fault injectionViewBoxis able to detect corruption and recover from it using cloud dataUpon a crash, ViewBoxdownloads consistent versions of files from cloudCausal ordering is preservedPerf%00;ormance = trace replayReplay iphoto_viewand iphoto_edittraces from iBenchMeasure workload runtime and synchronization time