5 A cloud file gateway is a device or virtual appliance that presents familiar file shares over SMB or NFS to users and applications, while storing the actual data in object storage. Active files are cached locally for fast access, and the full data set lives in a central object store, either in a public cloud or on private S3-compatible storage. File gateways have become a popular way to replace branch office NAS, consolidate file data from many sites, extend file shares with near-unlimited capacity and simplify backup and disaster recovery. This article explains how cloud file gateways work, what they use object storage for, their common features and limitations, how to size them and when they are a good fit. For the broader NAS question, see our hub on when object storage can replace NAS. How a cloud file gateway works Local presentation The gateway exposes SMB or NFS shares on the local network. Users map drives and applications mount shares as they would with any NAS. Permissions typically integrate with Active Directory or other directory services. Local cache The gateway keeps recently used and frequently accessed files on local disks or flash. Reads of cached files are served at local network speed. Writes land in the cache first and are then uploaded to object storage. Object storage back end All file data, and often file system metadata, is stored in object storage. The gateway translates file operations into object operations, usually splitting files into chunks, deduplicating and compressing them and encrypting them before upload. Object storage becomes the authoritative copy. Metadata and namespace The gateway maintains the file system namespace, folder structure, permissions and file versions. In multi-site deployments, a global namespace lets users at different locations see the same files, with metadata synchronized through the object store or a coordination service. Common features Unlimited capacity: local shares can hold far more data than the gateway’s local disks, since everything lives in object storage. Global namespace: one set of shares visible from many sites. Snapshots and versioning: frequent, space-efficient snapshots stored in object storage, enabling quick recovery of deleted or overwritten files. Ransomware recovery: restoring shares to a point before encryption from immutable snapshots. Cross-site file locking: some gateways coordinate locks across sites to prevent conflicting edits. Deduplication, compression and encryption before data leaves the site. Edge-to-core consolidation: branch NAS replaced by small gateways, with data centralized. Why object storage is the back end Object storage gives gateways a durable, scalable, cost-efficient home: Durability: erasure coding and multi-site replication protect data far better than a branch NAS. See erasure coding vs replication. Scale: capacity grows centrally by adding nodes, without upgrading every branch. Immutability: object lock can protect snapshots from deletion. Centralized protection: data in the object store can be protected and replicated in one place, often eliminating separate branch backups. Public cloud or private object storage? Gateways can use public cloud object storage or private S3-compatible storage in the organization’s own data centers: Public cloud avoids running central storage but adds ongoing storage, request and egress costs, and raises data location questions. Private object storage keeps data on infrastructure the organization controls, avoids request and egress fees and supports data sovereignty requirements. Branches still benefit from local caching. Many organizations in Europe, Japan and the Middle East, and public sector bodies everywhere, choose private object storage for file data that must remain in-country. See how distributed offices share files on private object storage. Limitations to understand Cache misses: accessing uncached files requires fetching data from object storage, which can be slow over limited WAN links, especially for large files. Upload backlog: heavy writes at a site can build a backlog if WAN bandwidth is insufficient, leaving data temporarily only on the gateway. Data format: gateways usually store data in their own chunked format, so files are not directly readable as objects over S3 without the gateway. Application compatibility: most file applications work, but some with demanding locking or latency requirements may not. Vendor dependence: since data is stored in the gateway’s format, moving to another gateway product requires migration. Sizing a gateway deployment Cache size Size the local cache to hold each site’s active working set, typically recent and frequently used files, with headroom. Too small a cache causes frequent misses and slow access. WAN bandwidth Bandwidth must handle daily change uploads, cache misses and initial data loads. Model peak write rates and how long backlogs can be tolerated. Object storage capacity Total file data across sites plus snapshots, versions, growth and protection overhead, minus deduplication and compression savings. Central throughput The object store must handle concurrent uploads and downloads from all gateways, especially during initial migrations or site recoveries. See storage capacity planning. Use cases Branch office NAS replacement: small gateways at each site with central object storage. Collaboration across sites: engineering, design and media teams sharing large files through a global namespace. NAS capacity extension: offloading cold data from existing NAS while keeping access. Disaster recovery: rebuilding a site’s file shares from the object store onto a new gateway. Backup consolidation: replacing branch backups with central snapshots and replication. Designing the central object store for gateways The central object store carries every site’s data, so design it as critical infrastructure: Multi-site protection: replicate or distribute the object store across at least two data centers so a single site failure does not take every branch’s files offline. Throughput for recovery: when a branch gateway fails, rebuilding its cache from the object store should be fast, so plan download capacity as well as upload capacity. Separate buckets or accounts per site or business unit for clearer reporting, access control and lifecycle policies. Object lock for snapshot data, protecting against deletion by compromised gateway or administrator credentials. Monitoring of request rates, latency and capacity per gateway. How gateways handle conflicts When the same file is edited at two sites, gateways resolve conflicts in different ways. Some use global file locking, so only one site can edit at a time. Others allow concurrent edits and keep both versions, flagging a conflict for users to resolve. Engineering and design teams working on large shared files usually need locking; general office shares may tolerate conflict copies. Understand how your chosen gateway behaves and set user expectations accordingly. Operations and monitoring Monitor cache hit rates, upload backlogs, WAN utilization, snapshot schedules and object storage health. Alerts for growing backlogs are especially important, since they indicate data that exists only on a local gateway and is not yet protected centrally. Keep gateway software current, since updates often improve performance and security. Migration to a gateway Migrating from NAS to a gateway typically involves copying data into the gateway, which uploads it to object storage, while preserving permissions and timestamps. Large data sets may be seeded centrally to avoid saturating WAN links. Plan cutovers per site with communication to users. Cost comparison Compare a gateway design with branch NAS refreshes over five years, including hardware at every site, local backups, site visits, central storage, gateways and WAN upgrades. Centralizing data usually reduces total cost and risk once more than a handful of sites are involved. Checklist: cloud file gateway Identify sites, shares, users and applications in scope. Choose public cloud or private object storage based on cost and data location. Size cache for each site’s active working set. Size WAN bandwidth for uploads, misses and initial loads. Size central object storage for capacity and throughput. Configure snapshots, versioning and immutability. Validate applications that need locking or low latency. Plan migration, seeding and per-site cutovers. Understand data format and exit options. Putting it together A cloud file gateway gives users familiar file shares while putting the data in scalable, durable object storage. It replaces branch NAS, enables multi-site collaboration, simplifies backup and makes ransomware recovery faster. Pair gateways with private S3-compatible object storage when cost predictability and data location matter, size caches and WAN links carefully and validate demanding applications before migrating. Frequently asked questions What is a cloud file gateway? A device or virtual appliance that serves SMB or NFS shares locally, caching active data, while storing all data in object storage. Does a file gateway need public cloud? No. Many gateways work with private S3-compatible object storage in the organization’s own data centers. What happens if a file is not in the gateway cache? The gateway fetches it from object storage, which takes longer than a cached read, depending on file size and network. Can gateways protect against ransomware? Many offer frequent immutable snapshots stored in object storage, enabling shares to be restored to a point before an attack. Can I read gateway data directly from object storage? Usually not, because gateways store data in their own chunked, deduplicated format. Further reading See when object storage can replace NAS, moving cold data off NAS filers, NFS and SMB access to object storage, distributed office file sharing and redefining NAS from edge to core.
