Speakers
Description
XRootD-Ceph is a storage plugin that allows one to access Ceph object store via xroot protocol. At RAL, we use this plugin for our disk SE. Although it has proven to be suitable for production-quality high-throughput storage, a few optimizations were needed to ensure optimal performance. In this talk we discuss the evolution of the plugin at RAL.
Some changes to the plugin were dictated by operational issues. The plugin is based on the Rados striper library, which is designed to handle complex access patterns (e.g., simultaneous read/write operations for the same file by multiple clients), and that impacts performance. We found that certain read operations (so-called vector reads) can be very slow, causing operational problems. To fix this, we changed the plugin so that it bypasses the striper and uses lower-level requests for reads.
Other changes are driven by the need to improve storage throughput for HL-LHC. Although this work is ongoing, we have already implemented a streamed check sums mechanism (when a check sum is calculated “on the fly” while the file is being uploaded rather than after the completion of the upload), as well as low-level writes that bypass Rados striper library. In this talk we compare the performance gains of these new features.