31 March 2014

Storage thoughts from GRIDPP32

Last week saw me successfully talk about the planned CEPH installation at the RAL Tier1. Here is a list of other thoughts which came up form GRIDPP32:

ATLAS and CMS plans for Run2 of the LHC seems to have an increase in churn rate of data at their Tier2s which will lead to a higher deletion rate being needed. Also will need to look at making sure dark data is discovered and deleted in a more timely manner.

A method for discovering and deleting empty directories which are no longer needed needs to be created. As an example at the Tier1, there are currently 1071 ATLAS users , each of whom can create  up to 131072 sub-directories which can end up being dark directories under ATLAS's new RUCIO namespace convention.

To help with deletion, some of the bulk tools the site admins can use are impressive (but also possible hazardous.) One small typo when deleting may lead to huge unintentional data loss!!!

Data rates shown  by Imperial college  of over 30Gbps WAN traffic are impressive (and makes me want to make a comparison between all UK sites to see  what rates have been recorded via the WLCG monitoring pages.

Wahid Bhimji's  storage talk also got me thinking again that with the rise of the WLCG VO's  FAX/AAA systems and their relative increase in usage; perhaps it is time to re-investigate WAN tuning not only of WN's at sites but also of XROOT proxy servers used by the VOs. In addition, I am still worried about monitoring and controlling the number of xrootd connections per disk server in each of the type's of SE  which we have deployed on the WLCG.

I was also interested to see his work using DAV and its possible usefulness for smaller VOs.

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