Abstract
We proposed a disk-based custodial storage as an alternative to tape for the ALICE experiment at CERN to preserve its raw data. The proposed storage system relies on Redundant Array of Independent Nodes (RAIN) layout – the implementation of erasure coding in the EOS storage suite, which is developed by CERN – for data protection and takes full advantage of high-density Just-Bunch-Of-Disks (JBOD) enclosures to maximize storage capacity as well as to achieve cost-effectiveness comparable to tape. The system we present provides 18 PB of total raw capacity from the 18 set of high-density JBOD enclosures attached to 9 EOS front-end servers. In order to balance between usable space and data protection, the system will stripe a file into 16 chunks on the 4-parity enabled RAIN layout configured on top of 18 containerized EOS FSTs. Although the reduction rate of available space increases up to 33:3% with this layout, the estimated annual data loss rate drops down to 8:6 × 10−5%. In this paper, we discuss the system architecture of the disk-based custodial storage, 4-parity RAIN layout, deployment automation, and the integration to the ALICE experiment in detail.
Highlights
The ALICE experiment [1] is one of the four gigantic experiments being performed using the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN), to study the nature of primordial matter, the Quark-Gluon Plasma, believed to be formed just after the Big Bang
Like the other giant experiments at CERN such as ATLAS, CMS, and LHCb, the ALICE experiment mainly relies on the Worldwide LHC Computing Grid (WLCG) [2] for its asynchronous processing of data produced from proton-proton or protonnucleus or nucleus-nucleus collisions at the LHC
As our custodial storage system is based on cheap JBOD enclosures purchased without any vendor enterprise-class solutions or any relevant technical support contracts for the system administration and management for monitoring and alerting, we rely on S.M.A.R.T (SelfMonitoring, Analysis and Reporting Technology) information provided by an open-source tool such as smartmontools [18] or a Linux CLI tool such as sg_ses for hardware-level monitoring and fault detection
Summary
The ALICE experiment [1] is one of the four gigantic experiments being performed using the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN), to study the nature of primordial matter, the Quark-Gluon Plasma, believed to be formed just after the Big Bang. A Hierarchical Storage Management (HSM) system including disk buffer should be placed in front of tape to read and write data, and an organized way of access requests is mandatory to complement the serial access of tape through drives. In 2018 at the Korea Institute of Science and Technology Information (KISTI) in South Korea - a WLCG Tier-1 centre for the ALICE experiment - we proposed a disk-based custodial storage system for the experiment as an alternative to tape. A preliminary design has been presented [7], based on high-density Just-Bunch-Of-Disks (JBOD) enclosures accommodating erasure coding implementation in EOS, together with the study on performance limitation of 12 Gbps SAS HBA, and demo equipment test results including I/O performance and power consumption compared to the tape library as well as other enterprise-class disk storage running at KISTI Tier-1 centre. We discuss in detail the system architecture, targeting a production service for ALICE experiment in mid-2021, based on EOS implementation of erasure coding for data protection
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