Louhi has several local disks for system files and computational data.  The most important one for Louhi users is the work disk, under /wrk directory, where all users have a personal directory specified by the $WRKDIR variable. All computational work should be performed in $WRKDIR for performance reasons and because compute nodes see only Lustre file systems. The file system in /wrk is Lustre, a high-performance parallel file system designed to handle the huge I/O demands of  parallel programs.

Another Lustre files system is /fs/local, which is also seen in the compute nodes. Every user have the directory /fs/local/users/user_id where users can keep their programs and data if they are needed in near future. $WRKDIR is cleaned regularly and files older than 4 weeks are removed.

The compute nodes do not have any local disks, all disks are accessed over the Cray SeaStar2 communication interconnect. Each service I/O node has two fibre channel (FC) cards with two FCs per card. These service I/O nodes provide other nodes access to /wrk disk and system disks. /wrk disk is served by a Engenio 6998 storage system comprising of two cabinets providing approximately 67 TB of space. The cabinets have 288 drives (300 GB a piece), grouped in 8+1 RAID 5 configurations. The theoretical read/write speed is 3.2 GB/s, and in practice speeds over 2 GB/s can be achieved. In addition, there is also a Engenio 3992 storage system serving system disks.