Data Management Glossary
Stubs
What are Stubs?
Stubs are placeholders of the original data after it has been migrated to secondary storage. They replace archived files in the location selected by the user during the archive process. Because stubs are proprietary and static, if a stub file is corrupted or deleted, the moved data becomes orphaned. This creates a risk of disruption to users, applications or data protection workflows.
Stubs are commonly used to make tiered data appear as if it still resides on primary storage. However, this approach introduces architectural limitations and operational risks, particularly at scale.
Komprise does not use stubs. Komprise Intelligent Data Management uses patented Transparent Move Technology, which relies on industry-standard symbolic links and uses Dynamic Links instead of proprietary stubs, so tiered files remain directly accessible without rehydration or the risks described below.
Stubs are commonly used to make tiered data appear as if it still resides on primary storage. However, this approach introduces architectural limitations and operational risks, particularly at scale.
How do stubs work after data is migrated to secondary storage?
Stubs act as placeholders for the original files once data has been archived or moved to secondary storage. When users access stubbed data, the storage management system intercepts the request, retrieves the data from its secondary location, whether file, object, cloud, or tape and rehydrates it back to primary storage. While this makes tiered data appear to reside on primary storage, the transparency ends there. The retrieval and rehydration process adds latency and increases the risk of data loss or corruption.
What are the risks and challenges associated with using proprietary stubs?
Stubs are brittle. When stubbed data is moved from its storage location to another system, the stubs can break. Once broken, the storage management system no longer knows where the data resides and the data becomes orphaned, preventing access. Because stubs are proprietary and static, corruption or deletion of the stub file directly impacts access to the migrated data.
Most storage management solutions that use stubs rely on client-server architecture and do not scale effectively to support data at massive scale. This creates operational challenges in large environments where data movement and growth are continuous.
Why do proprietary stub-based approaches limit transparency and scalability?
Proprietary interfaces such as stubs are used to make tiered data appear as though it remains on primary storage, but true transparency is not achieved. The storage management system must intercept access requests and rehydrate data, which introduces additional processing, latency, and operational complexity.
Because stubs are not based on open standards, they create dependency on a specific system. This limits flexibility and increases the risk of disruption if the stub file is altered, deleted or if data is moved outside the control of the storage management platform.
How does standards-based transparent data tiering differ from stub-based methods?
A true transparent data tiering solution creates no disruption, and that is only achievable with a standards-based approach. Komprise Intelligent Data Management uses Transparent Move Technology™ (TMT), which relies on Dynamic Links based on industry-standard symbolic links instead of proprietary stubs.
By using standards-based symbolic links rather than static proprietary stubs, the risk of orphaned data and broken access paths is eliminated. This approach maintains transparency without introducing latency, disruption, or the brittleness associated with traditional stub-based systems.
Stubs are proprietary placeholders used after data is migrated to secondary storage, but they introduce risks such as orphaned data, latency, and limited scalability. Because stub-based systems rely on static and brittle mechanisms, they can disrupt users and applications when data is moved or modified. Standards-based transparent data tiering using symbolic links provides a more resilient and scalable alternative without the operational risks of proprietary stubs.
Learn more about the differences between stubs, symbolic links and Dynamic Links from Komprise.
Read the Komprise Architecture Overview white paper to learn more.
How Komprise finds data without relying on stubs
Stub-based systems need to intercept a file access request to know where the data actually lives, which is part of why they introduce latency and fragility. Komprise avoids this by maintaining visibility separately from the file path. The Global Metadatabase indexes every file across NAS, cloud, and object storage, tracking where each file lives and what it is, independent of any placeholder sitting in the original folder. When a policy calls for a file to move, Komprise uses Transparent Move Technology to relocate it and leaves a standards-based Dynamic Link behind, so both the file system and the person or application accessing it stay in sync without depending on a fragile proprietary reference.
This distinction matters more as flash storage costs rise. Gartner is calling the current memory price surge Memflation, with NAND flash prices forecast to increase 234% in 2026. Organizations moving more cold data off primary storage to manage that cost pressure are moving more files, more often, which is exactly the scenario where a brittle, stub-based approach accumulates risk.
Source: Gartner, “Gartner Forecasts Worldwide Semiconductor Revenue to Exceed $1.3 Trillion in 2026,” April 8, 2026
| Evaluation Criteria | Stub-Based Tiering | Komprise Dynamic Links |
|---|---|---|
| Underlying mechanism | Proprietary placeholder file specific to one vendor’s storage management system | Industry-standard symbolic link, part of Transparent Move Technology |
| Risk if the placeholder breaks or moves | Data becomes orphaned, storage system loses track of its location | Standards-based and portable, no dependency on a single vendor’s system |
| Rehydration required to access data elsewhere | Yes, full rehydration back to primary storage | No, files remain directly accessible at their new location |
| Scalability | Client-server architecture, limited at massive file counts | Global Metadatabase, proven across billions of files at petabyte scale |
| Vendor lock-in | Tied to the originating storage system | Works across NetApp, Dell, Everpure, Qumulo, and cloud storage |
STUB FAQs
Does Komprise use stubs?
No. Komprise Intelligent Data Management uses Transparent Move Technology, which relies on industry-standard symbolic links called Dynamic Links, not proprietary stubs.
What is the difference between a stub and a symbolic link?
A stub is a proprietary placeholder tied to a specific vendor’s storage management system. A symbolic link is an open, industry-standard file system reference that works independently of any single vendor, which is why Komprise Dynamic Links avoid the lock-in and fragility associated with stubs.
What happens if a stub file is deleted or corrupted?
The data it points to becomes orphaned. Because stubs are proprietary and static, the storage management system loses track of where the original file lives, and access is disrupted until the reference is repaired or the data is recovered another way.
How does Komprise avoid the rehydration penalty associated with stubs?
Files moved by Komprise stay in their native format at the new location and remain directly accessible through Dynamic Links. There is no need to move the file back to primary storage before it can be read, backed up, or processed by another application.
Does Dell EMC Isilon CloudPools use stubs?
Yes. Isilon CloudPools references tiered files using stubs, which ties access back to the original Isilon or PowerScale array and requires rehydration for functions like backup by an external application or migration to a new array.