This dataset is a reduced size version of an Illumina NovaSeq run of PhiX, where all but the first four cycles have been removed. All metadata associated with the run has been kept intact. This dataset is e.g. useful in testing workflows which require raw Illumina data (i.e. bcl files rather than fastq files). To demultiplex this data with Illumina bclfastq (https://support.illumina.com/sequencing/sequencing_software/bcl2fastq-conversion-software.html) it is recommended that the following options are used: --ignore-missing-bcls --ignore-missing-filter --ignore-missing-positions --use-bases-mask y4n*,n* This work was supported by the R&D group at the SNP&SEQ Technology Platform in Uppsala. This facility is part of the National Genomics Infrastructure (NGI) Sweden and Science for Life Laboratory. The SNP&SEQ Platform is also supported by the Swedish Research Council and the Knut and Alice Wallenberg Foundation.