Glossary
Cloud storage gateway
A cloud storage gateway is a physical or virtual appliance that lets applications use object storage as if it were a local file share, disk or tape library. It translates those familiar protocols into object requests and keeps recently used data in a local cache.
Three gateway modes
| Mode | What the application sees | How data lands in the object store | Readable without the gateway |
|---|---|---|---|
| File | A network share | Usually one file per object, with its name | Generally yes |
| Block | A disk volume | Chunks stored under internal identifiers | No |
| Tape | A virtual tape library | Virtual tapes split into chunks | No |
The last column matters most at the end of a gateway's life. Data written in block or tape mode can only be reassembled by the gateway that wrote it, which ties every later cloud migration to that software. A file gateway that keeps names and contents intact leaves objects any S3 client can read.
The cache sets the speed
Reads served from the local cache return at local speed. Reads that miss travel to the object store and back and are much slower, so the match between cache size and the working set decides how fast the system feels. The difference shows up directly in storage latency measurements, and a cache sized for last year's working set is a common cause of complaints that arrive gradually.
When is a write actually safe?
In write-back mode the gateway confirms a write once it reaches the cache and uploads it later. Until the upload queue drains, the gateway holds the only copy. As a worked example, 2 TB waiting behind a 1 Gb/s link needs roughly four and a half hours to clear at full use of the link, and a cache failure in that window loses whatever had not been sent. Queue depth is therefore worth monitoring and alarming on. Write-through mode confirms only after the upload, which closes the window and adds latency to every write.
A bridge for software that cannot change
Gateways exist for applications fixed to a file share or a tape library. New applications write to object storage directly and avoid the cache, the queue and the extra hop. Systems that offer several access methods natively, described under multi-protocol storage, remove the translation layer without changing how older applications connect.