CTA 5 and HTTP Tape API

Hi all,

I saw from the Tape REST API slides at the XRootD and FTS workshop that the LHCb production CERN CTA instance appears to support the HTTP Tape API (slide 5). This is excellent news, but it did raise a few questions:

  1. Does this mean CERN are running CTA with EOS 5.X in production? Is this recommended for other sites currently?
  2. I’m a little confused by the interaction between CTA versions and EOS versions. From comparing recent 5.x.y and 4.x.y tags it looks like it’s the same CTA code (or at least the same recent commits), and the CTA major version is just defining which XRootD and EOS versions should be/are used. Have I got this right?
  3. If so, would an upgrade path to the HTTP Tape API look something like:
    • an upgrade to a recent CTA 4.X version and the appropriate EOS 4 version
    • upgrade your EOS clusters to 5 (and CTA to 5, although this shouldn’t change anything on the CTA side)

I’d appreciate being put straight on anything that is completely wrong here, we’re keen to get this all understood so we’re clear on our route to the HTTP Tape API.


George just pointed out that later EOS 4 releases appears to have the HTTP REST Tape API features, so these questions may be entirely misplaced!

Some clarification on what CERN are running in production to enable the HTTP REST Tape API, and what the upgrade path to EOS and CTA 5 looks like would still be appreciated if possible.


Hi Tom,

  1. No, we run EOS4. EOS5 should be fine, but we are not using it in production, therefore we don’t guarantee it to be fully stable together with CTA.
  2. Yes, but only regarding XRootD. 5.x.y uses XRootD version 5, 4.x.y uses version 4. The EOS version is independent. We are still using CTA 4.x in production, we will upgrade to 5.x in the next months.
  3. To get the REST API features, you should install EOS 4.8.88 or later. The CTA version does not matter, as all the REST API features are in EOS.

Best regards,

Hi Jorge,

Brilliant, thanks for the clarification.

Happily we are already running EOS 4.8.88, and hadn’t twigged that we were in a position to try the REST API out - we’ll be testing on a dev cluster as soon as possible!