CERN IT Department CH-1211 Genève 23 Switzerland t Xrootd through WAN… Can I? Now my WAN is well tuned! So what? Now my WAN is well tuned. So what? (Xrootd advancements on the “Long, fat pipe problem”)

CERN IT Department CH-1211 Genève 23 Switzerland t Step 1: Tune it ! Costin’s recipe can boost the efficiency of WANs –More precisely, it makes its usage much less inefficient By giving the correct TCP parameters to the kernel Need to fix client and server machines –Everybody will be happier But then?

CERN IT Department CH-1211 Genève 23 Switzerland t WANs are difficult In WANs each client/server response comes much later –E.g. 180ms later With well tuned WANs one needs apps built with WANs in mind –Otherwise they are walls impossible to climb I.e. VERY bad performance –Bulk xfer apps are OK (gridftp, xrdcp, fdt, etc.) –There are more interesting use cases, and much more benefit to get XROOTD and ROOT are OK

CERN IT Department CH-1211 Genève 23 Switzerland t A simple use case I am a physicist, waiting for the results of my analysis jobs –Many bunches, several outputs Will be saved e.g. to ALICE::CERN::SE –My laptop is configured to show histograms etc, with ROOT –I leave for a conference, the jobs finish while in the plane –When there, I want to simply draw the results from my Alien home directory –When there, I want to save my new histos in the same place –I have no time to loose in tweaking to get a copy of everything. I loose copies into the confusion. I know nothing about parameters to tweak. What can I expect? Can I do it? I know nothing about parameters to tweak. What can I expect? Can I do it?

CERN IT Department CH-1211 Genève 23 Switzerland t Another use case ALICE analysis on the GRID Each job reads ~150MB from ALICE::CERN::SE Difficult to put location-dependent tweaks in jobs It would be nice to speed it up –At 5MB/s it takes 20secs –At 1MB/s it takes 100 Sometimes data are accessed elsewhere –It would be nice if it was more efficient Better usage of resources, more processed jobs/day After all, ROOT/ALIROOT is not able to r/w data at more than 20MB/s with 100% usage of 1 core This fits perfectly with the current WAN status

CERN IT Department CH-1211 Genève 23 Switzerland t Up to now Up to now it was possible –But it needed a tweak to enable/disable the WAN mode of XrdClient So, difficult to automatize. Very technical, hence nobody cares! Now the things are much better –The good old WAN mode is OK for bulk xfers –The new improvements use the possibilities of the newer kernels and TCP stacks –Interactive things should need nothing So, if you have: –The new client (to appear in ROOT next week) –A new server (available through xrd-installer) With the new fixed configuration! –You can expect a good improvement over the past Without doing nothing special, no tweaks

CERN IT Department CH-1211 Genève 23 Switzerland t Heavy drawing/reading 180ms RTT (Caltech machinery) Very well tuned kernels

CERN IT Department CH-1211 Genève 23 Switzerland t Writing and overheads 180ms RTT (Caltech machinery) Very well tuned kernels

CERN IT Department CH-1211 Genève 23 Switzerland t Conclusion Things look very good –BTW same order of magnitude than a local RAID disk (and who has a RAID in the laptop?) –Writing gets really a boost Aren’t job outputs written that way sometimes? Even with Tfile::Cp And they are on by default, but they need: –Well configured client and server machines –Xrootd client and server (the newest) –An app for which it makes sense, e.g. ROOT with well designed data Alien