{"licence":{"name":"CC BY-SA 4.0","spdx":"CC-BY-SA-4.0","url":"https://creativecommons.org/licenses/by-sa/4.0/","attribution":"Atlas, a bilingual technical dictionary (https://atlas.maintz.dev/)"},"id":"security/backup","url":{"en":"https://atlas.maintz.dev/en/terms/security/backup/","da":"https://atlas.maintz.dev/da/terms/security/backup/"},"term":{"en":"Backup","da":"Backup"},"aka":{"en":["backup copy","data backup"],"da":["sikkerhedskopi","sikkerhedskopiering"]},"domain":["security","cs"],"cluster":"controls","layer":"data","status":"current","summary":{"en":"A separate copy of data kept so it can be restored after a breakdown, a mistake or an attack.","da":"En separat kopi af data, som gemmes, så de kan gendannes efter nedbrud, fejl eller angreb."},"body":{"formal":{"en":"A copy of data and system settings taken on a schedule and stored apart from the original - ideally with at least one copy offline - and regularly tested by actually restoring from it.","da":"En kopi af data og systemindstillinger, der tages efter en fast plan og opbevares adskilt fra originalen - helst med mindst én kopi offline - og som jævnligt testes ved faktisk at gendanne fra den."},"plain":{"en":"Like keeping paper copies of your passport and deeds at a relative's house - if your home burns down, the papers are not lost.","da":"Som at have kopier af pas og skøde liggende hos et familiemedlem - hvis dit hus brænder, er papirerne ikke tabt."},"inPractice":{"en":"Ransomware locks a municipality's file server on a Monday; because last night's copy sat on a disk that was not connected, the IT operations team wipes the server and restores the files by lunchtime.","da":"Ransomware låser en kommunes filserver en mandag; fordi nattens kopi lå på en disk, der ikke var tilsluttet, sletter IT-driften serveren og har gendannet filerne ved frokosttid."},"whyItMatters":{"en":"It is the last line of defence for availability - when everything else fails, a tested copy decides whether the business loses hours or loses everything.","da":"Det er sidste forsvarslinje for tilgængeligheden - når alt andet svigter, afgør en testet kopi, om virksomheden mister timer eller mister alt."}},"deepDive":{"en":"Backup design starts from two numbers agreed with the business: the recovery point objective (RPO, how much data loss in time is tolerable) and the recovery time objective (RTO, how long restoration may take). RPO drives backup frequency and technique - nightly full or incremental jobs, continuous journaling, database transaction-log shipping - while RTO drives the restore path: instant VM recovery from a backup repository, bare-metal restore, or rebuilding from infrastructure-as-code and then restoring data. Classic job types are full, incremental (changes since the last backup of any kind) and differential (changes since the last full); modern systems create \"synthetic fulls\" by merging increments on the repository and use block-level change tracking and deduplication to keep windows short.\n\nThe 3-2-1 rule - three copies, on two different media, one off-site - is often extended to 3-2-1-1-0: one copy offline, air-gapped or immutable, and zero errors in verified restores. Immutability is now the main ransomware defence, because modern ransomware operators deliberately locate and delete backup catalogues, shadow copies and repository credentials before encrypting. Implementations include object storage with WORM retention (for example S3 Object Lock in compliance mode, which even the root account cannot shorten), hardened Linux repositories with immutable file flags, tape rotated off-site, and backup systems in a separate administrative domain with their own MFA-protected credentials. Snapshots on the same storage array, RAID and synchronous replication are not backups: they faithfully replicate deletion, corruption and encryption.\n\nConsistency matters as much as existence. A crash-consistent image of a running database may not start; application-consistent backups quiesce writes (on Windows via VSS writers) or use the database's own dump or log mechanism. SaaS data is a frequent gap - under the shared-responsibility model, providers such as Microsoft 365 guarantee service availability but offer limited retention of user-deleted or maliciously altered data.\n\nNormative anchors: CIS Controls v8 Control 11 (Data Recovery), including an isolated instance of recovery data (Safeguard 11.4) and restore tests of a sample of assets at least quarterly (11.5); ISO/IEC 27002:2022 control 8.13 (information backup); NIS2 Art. 21(2)(c), which lists backup management alongside business continuity and disaster recovery; and GDPR Art. 32(1)(c), the ability to restore availability and access to personal data in a timely manner. Retention also has a data-protection side: backups containing personal data are subject to storage limitation, and erasure requests are usually handled by documented expiry rather than editing old backup sets. The only real evidence a backup works is a timed, documented restore.","da":"Backupdesign begynder med to tal, der aftales med forretningen: recovery point objective (RPO, hvor meget datatab målt i tid der kan accepteres) og recovery time objective (RTO, hvor lang tid gendannelsen må tage). RPO bestemmer hyppighed og teknik - natlige fulde eller inkrementelle job, kontinuerlig journalisering, forsendelse af databasens transaktionslog - mens RTO bestemmer gendannelsesvejen: instant recovery af VM'er direkte fra backup-repositoriet, bare-metal-gendannelse eller genopbygning fra infrastructure-as-code efterfulgt af gendannelse af data. De klassiske jobtyper er fuld, inkrementel (ændringer siden seneste backup af enhver art) og differentiel (ændringer siden seneste fulde); moderne systemer danner \"syntetiske fulde\" backups ved at flette inkrementer på repositoriet og bruger ændringssporing på blokniveau og deduplikering for at holde backupvinduerne korte.\n\n3-2-1-reglen - tre kopier, på to forskellige medier, én uden for huset - udvides ofte til 3-2-1-1-0: én kopi offline, air-gapped eller uforanderlig (immutable), og nul fejl i verificerede gendannelser. Uforanderlighed er i dag det vigtigste værn mod ransomware, fordi moderne ransomwaregrupper bevidst finder og sletter backupkataloger, skyggekopier og adgangsoplysninger til repositorier, før de krypterer. Implementeringer omfatter objektlagring med WORM-opbevaring (fx S3 Object Lock i compliance mode, som ikke engang root-kontoen kan forkorte), hærdede Linux-repositorier med immutable-flag på filerne, bånd, der roteres ud af huset, og backupsystemer i et separat administrativt domæne med egne MFA-beskyttede konti. Snapshots på samme storage-system, RAID og synkron replikering er ikke backup: de gengiver trofast sletning, korruption og kryptering.\n\nKonsistens er lige så vigtig som eksistens. Et crash-konsistent image af en kørende database starter måske ikke; applikationskonsistente backups fastfryser skrivninger (på Windows via VSS-writers) eller bruger databasens egen dump- eller logmekanisme. SaaS-data er et hyppigt hul - under modellen for delt ansvar garanterer udbydere som Microsoft 365 tjenestens tilgængelighed, men tilbyder kun begrænset opbevaring af data, som brugere har slettet eller angribere har ændret.\n\nNormative ankre: CIS Controls v8 Control 11 (Data Recovery), herunder en isoleret kopi af gendannelsesdata (Safeguard 11.4) og gendannelsestest af et udsnit af aktiverne mindst kvartalsvist (11.5); ISO/IEC 27002:2022 kontrol 8.13 (backup af information); NIS2 art. 21, stk. 2, litra c, der nævner backupstyring sammen med driftskontinuitet og katastrofeberedskab; og databeskyttelsesforordningens art. 32, stk. 1, litra c, om evnen til rettidigt at genoprette tilgængeligheden af og adgangen til personoplysninger. Opbevaringen har også en databeskyttelsesside: backups med personoplysninger er omfattet af princippet om opbevaringsbegrænsning, og anmodninger om sletning håndteres typisk ved dokumenteret udløb frem for ved at redigere gamle backupsæt. Det eneste reelle bevis på, at en backup virker, er en tidsmålt og dokumenteret gendannelse."},"howTo":{"steps":{"en":["Agree the RPO and RTO with the business owner of each system, so backup frequency and restore method follow from real needs.","Make an inventory of what must be backed up - servers, databases, configurations, endpoints with local data and SaaS data such as Microsoft 365 - and name an owner for each.","Follow the 3-2-1 rule of three copies on two different media with one off-site, and keep at least one copy offline or immutable.","Separate the backup system from daily administration with its own accounts, MFA and no trust to the production domain, so an attacker who takes the domain cannot delete the backups.","Use application-consistent backups for databases and critical applications, and encrypt copies that leave the building while keeping the keys available offline.","Check backup jobs every day and follow up failed or missed jobs the same day.","Test restores regularly, a sample at least every quarter and a full restore of a critical system at least once a year, and record the time taken and the result.","Set retention periods that meet both recovery needs and GDPR storage limitation, and document how old copies expire."],"da":["Aftal RPO og RTO med den forretningsansvarlige for hvert system, så backuphyppighed og gendannelsesmetode følger af de reelle behov.","Lav en oversigt over alt, der skal tages backup af - servere, databaser, konfigurationer, klienter med lokale data og SaaS-data som Microsoft 365 - og udpeg en ejer for hvert punkt.","Følg 3-2-1-reglen med tre kopier på to forskellige medier, hvoraf én ligger uden for huset, og hav mindst én kopi offline eller uforanderlig.","Adskil backupsystemet fra den daglige administration med egne konti, MFA og ingen tillid til produktionsdomænet, så en angriber, der overtager domænet, ikke kan slette backupperne.","Brug applikationskonsistente backups til databaser og kritiske applikationer, og kryptér kopier, der forlader huset, men hav nøglerne tilgængelige offline.","Tjek backupjobbene hver dag, og følg op på fejlede eller manglende job samme dag.","Test gendannelse jævnligt, et udsnit mindst hvert kvartal og en fuld gendannelse af et kritisk system mindst én gang om året, og notér tidsforbrug og resultat.","Fastsæt opbevaringsperioder, der både opfylder behovet for gendannelse og databeskyttelsesforordningens krav om opbevaringsbegrænsning, og dokumentér, hvordan gamle kopier udløber."]},"pitfalls":{"en":["Treating RAID, snapshots on the same storage or file synchronisation as backup.","Never testing restores, so the first real attempt happens in the middle of a crisis.","Keeping backups on the same domain and admin accounts as production, where ransomware operators can find and delete them.","Leaving SaaS data out because the cloud provider is assumed to take care of it."],"da":["At regne RAID, snapshots på samme storage eller filsynkronisering for backup.","Aldrig at teste gendannelse, så det første rigtige forsøg sker midt i en krise.","At have backupperne på samme domæne og administratorkonti som produktionen, hvor ransomwaregrupper kan finde og slette dem.","At udelade SaaS-data, fordi man går ud fra, at cloududbyderen tager sig af det."]},"guides":[{"title":"CIS Critical Security Control 11 - Data Recovery","url":"https://www.cisecurity.org/controls/data-recovery","publisher":"Center for Internet Security","tier":"standard"},{"title":"Principles for ransomware-resistant cloud backups","url":"https://www.ncsc.gov.uk/guidance/principles-for-ransomware-resistant-cloud-backups","publisher":"NCSC UK","tier":"official-doc"},{"title":"#StopRansomware Guide","url":"https://www.cisa.gov/stopransomware/ransomware-guide","publisher":"CISA","tier":"official-doc"},{"title":"Reducer risikoen for ransomware","url":"https://samsik.dk/publikation/reducer-risikoen-for-ransomware/","publisher":"Center for Cybersikkerhed (Styrelsen for Samfundssikkerhed)","tier":"official-doc","lang":"da"}]},"edges":[{"type":"kind-of","to":"security/control","confidence":"high","strength":"normal"},{"type":"mitigates","to":"security/ransomware","why":{"en":"With a clean copy stored apart, locked data can be restored without paying.","da":"Med en ren kopi opbevaret separat kan låste data gendannes uden at betale."},"confidence":"high","strength":"primary"},{"type":"used-with","to":"security/disaster-recovery-plan","confidence":"high","strength":"normal"},{"type":"used-with","to":"security/business-continuity-plan","confidence":"high","strength":"normal"},{"type":"used-with","to":"security/recovery-objectives","confidence":"high","strength":"normal"},{"type":"used-with","to":"cs/database","confidence":"high","strength":"normal"}],"depth":0,"sources":[{"title":"Cyber Security Fast Track - Ordliste","tier":"course-material"},{"title":"CIS Critical Security Controls v8 - Control 11 (Data Recovery)","tier":"standard","publisher":"Center for Internet Security"}],"draft":true}