The first disk-based custodial storage for the ALICE experiment

<!--HTML-->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 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 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 $8.6 \times 10^{-5}\%$. 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.