hesela.devSIS link
A SIS link is a sparse NTFS file with a reparse point through which Single Instance Storage presents private file contents backed by shared common-store data.
The reparse payload is opaque to backup software and is handled through SIS APIs. A link is not a hard link: its user-visible file can diverge while shared backing data remain unchanged. [1]
During restore, SisRestoredLink requires unallocated ranges to remain unallocated, not filled with zeroes. It returns each needed backing file at most once; an empty result can mean already reported, not already restored. [2]
After restoring a requested backing file, call SisRestoredCommonStoreFile to let SIS repair its internal structures and links. Track requested dependencies through completion rather than treating discovery as a data-transfer receipt. [3]
Relations
- related
- Copy-on-close, Sparse file, Data deduplication
Advantages
- Repeated links can share backing data, reducing duplicate backup transfers. [4]
Limitations
- Restoring the link name and reparse metadata alone does not supply missing common-store contents. [1, 2]
- The 2000 paper's deferred copy-on-close and the later overview's pre-write copying are distinct descriptions; neither establishes current Windows support. [6, 5]
Citations
- Microsoft: SIS Links and Reparse Points, sparse representation and opaque metadata
- Microsoft: SisRestoredLink, sparse ranges and once-per-operation dependency reporting
- Microsoft: SisRestoredCommonStoreFile, reporting restored backing files
- Microsoft: SisCSFilesToBackupForLink, shared-file discovery
- Microsoft: The SIS Common Store and Common-Store Files
- Bolosky, Corbin, Goebel and Douceur (2000). Single Instance Storage in Windows 2000, USENIX Windows Systems Symposium, pp. 13-24, sections 2.3.3-2.3.5.
Further reading
Sources & caveats
- Historical source synthesis of the Windows 2000 SIS paper and Microsoft backup API documentation, reviewed 2026-11-05. No Windows restore, mapped-I/O or failure-injection experiment was performed.