Protocol Cheat Sheet
This is a quick reference of the different protocols supported by GFAL2.
| Protocol | Auth | Data Transfer | Space Tokens* | Third Party Copy | Staging/QoS | Notes |
|---|---|---|---|---|---|---|
| lfc | X509 | NO | NO | NO | NO | Deprecated. Maintained by DPM team. |
| srm | X509 | NO | YES | NO | YES | XML-Based. Some calls are asynchronous (token-based) |
| gsiftp | X509 | YES | NO | YES | NO | Async API (callbacks). Maintained by Globus, to be adopted by OSG. |
| xrootd | X509, Kerberos | YES | As part of the URL | YES | YES, EOS/CTA | Async and sync API (Posix-like). |
| http/dav | X509, Tokens | YES | As part of the URL | YES | YES, CDMI-QoS | DAV is XML-Based. Copies may fallback to streaming if neither endpoint support copies. |
| s3 | X509, Tokens, AWS Signature | YES | As part of the URL | Only as passive endpoint | NO | Implemented by HTTP-plugin via Davix. |
| rfio | X509, by hostname | YES | NO | NO | NO | Deprecated. Maintained by DPM. |
| dcap | X509 | YES | NO | NO | NO | Deprecated. dCache-specific. |
| dropbox | OAuth2 | YES | NO | NO | NO | JSON-Based. |
| sftp | User/password or SSH private key | YES | NO | NO | NO | Experimental |
Transfers / copies
While namespace operations are relatively straight forward - just look at the URI and choose depending on the scheme -, transfers can get trickier, since they may involve different combinations of two protocols.
It is up to the plugins to decide whether they take over any transfer involving them or not. The following table summarizes what happens in each case.
| Source | Destination | Plugin | Explanation |
|---|---|---|---|
| srm | * | srm plugin | srm needs to resolve the transfer URL before doing the copy. Also, it handles space tokens. |
| * | srm | srm plugin | Same. |
| gsiftp | gsiftp | gsiftp plugin | Third party copies. |
| xrootd | file | xrootd plugin | More performant API call than read-write calls. |
| file | xrootd | xrootd plugin | Same. |
| xrootd | xrootd | xrootd plugin | Third party copies. |
| file | http | http plugin | One single PUT instead of chunk writes. |
| http | http | http plugin | Third party copies w/o fallback (push, pull, streamed). |
For any other combinations, gfal2 core takes over, and does the transfer via
open, read, write, close calls.
What is a space token?
A space reservation. Can be specified for the source and for the destination. The space reservation can be disk, and/or tape.
It is convenient to make a difference between two terms:
- Space token: An opaque ID, internal to the storage. It can be from an integer (dCache) to a UUID (DPM).
- Space token description: A human-readable label assigned to the space token. I.e. "ATLASSCRATCHDISK".
Normally users use "space token description".