Full backups of large storage devices are expensive, slow, and waste a lot ofspace. Incremental and differential backups are an oft-requested feature invirtualization stacks to help eliminate the redundant copying of backup data. This presentation will cover recent developments in related delta-backuptechnologies, covering incremental and differential backups, image fleecing,dirty bitmap management, and different paradigms of consuming this data toproduce reliable backups both through QEMU as an agent or via an externalbackup appliance. # Style This talk will cover the incremental backup functionality in QEMU anddevelopments since its first introduction in 2015. The talk is intended to be a fairly light-weight, quick trip through thefeature; explaining the mechanics behind both the implementation and the API.I do not intend to cover in incredible detail the algorithmic minutiae ofincremental backup techniques, but 'dirty bitmaps' as a fundamental technologyenabling the technique will feature quite heavily. A theme of the talk will behow these features were implemented using targeted modifications to existingstable API to unlock rich functionality while maintaining backwardscompatibility -- and the difficulties faced while doing so in a diverse opensource environment. Current/Future developments are intended to be a highlightof the talk. # Audience First and foremost, students who are interested in how large-scale projectstackle problems and would like some insight to how components in "the cloud"actually manage data on a technical level would find this talk interesting. Atthe very least, hopefully they find it entertaining. Secondly, any developers or hobbyists who rely on virtualization in theirworkflow, but may not be heavily invested or well-versed in QEMU/KVM/libvirtet al specifically could benefit from an expanded knowledge of how this FOSSvirtualization stack manages data. These users may be keen to gain insightinto newer, more flexible storage and backup options. Third, Upper-layer stack developers or users who script against upper-layervirtualization stack components may be interested to hear what we're cookingup -- this includes libvirt, virsh, openstack, oVirt or any projects thatcount these projects as dependencies. And lastly, anyone who has a keen appreciation for bad puns on slide captionsmight enjoy stopping by. # Takeaways Attendees can expect to leave with a basic outline of the storage managementsolutions as they exist in FOSS virtualization today, and how we'd like toimprove on them. With a copy of the slides and footnotes, attendees will bewell equipped to author power-user scripts that take advantage of someadvanced functionality in QEMU-kvm today that may help them eke out moremileage from their existing FOSS virtualization stack. The talk will covergeneral design, usage, current caveats and expected next steps for relatedbackup features; this will hopefully provide generally relevant informationfor anyone interested in or contributing to the field in general.