Time Machine backups do n’t add up ! Or , rather , if you ’re regard the contents of a Time Machine reliever volume in the Finder and chooseFile > Get Infoand enable work out All Sizes , the totals of all the snapshots typically far exceed the content of the mass . That ca n’t be — and it distract one reader whose shot were 1.7 TB — he thought he was running out of space on a 12 TB drive .
Apple ’s Time Machine is an idiosyncratic method acting of backing up volumes and furnish snapshot compared to how most cloning and archiving software plant and ever worked . Similar package typically makes an initial snapshot and then stores the interchange dowry of files along with a logarithm of deletion and folder changes . When you restore a Indian file , you ’re propose timestamped versions to choose among ; restore a snapshot and the software figures out which compounding of single file from the original snapshot it has to juggle with later changes to procreate the results .
Time Machine offers a unlike coming . Instead of build a unmarried comprehensive volume snapshot or single at long intervals and only storing differences , Time Machine creates the equivalent of timestamped virtual volume that appear when browsing a Time Machine volume to store every Indian file from the backed - up volume .
The substitute algorithm does make an initial snapshot to insure that every file and booklet on a loudness has a comparable entry on the Time Machine volume . After that , however , any filing cabinet that has n’t changed since the previous Time Machine backup is n’t replicate . Instead , the next backup creates a link to the original transcript of the file . When you graze a snapshot on a Time Machine book by afford a timestamped folder , it appear that every file is in the snap , not just the modified or unexampled ones . And the Finder swear on those links to do a calculation , make each snapshot folder seem to check the full solidification of files .
( A expert aside : With HFS+ volumes , Apple ’s long - running filesystem , these werehard links , a special form of one - to - many filesystem linking format . In Time Machine backup man to an APFS - formatted drive , Appleuses a form of central data storeand creates a link in Time Machine snapshots from that computer storage . The core is the same . )
Behind the conniption , Time Machine prunes elderly snapshots both over time and as the repositing in an allotted bulk fills up . You should always have the most late 24 hourly shot and the last rolling month ’s Charles Frederick Worth of daily snapshots . Time Machine retains hebdomadal shot older than a calendar month until it has to delete them .
If you want to know theactual amount of storageremaining on a Time Machine volume or occupied by a shot on the bulk :
This Mac 911 article is in response to a question submit by Macworld reader Jim .
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