StorageOS provides a block device on which a file system can be created. However who creates this file system affects what filesystems StorageOS can support.
When using StorageOS with the native driver, Kubernetes is responsible for running mkfs against the StorageOS block device. This means that any file system that Kubernetes can create can be used.
However if the StorageOS CLI is used to mount a device then an ext4 filesystem will be created by default.
When using StorageOS with the CSI driver, StorageOS is responsible for running mkfs against the block device that pods mount. StorageOS is able to create ext2, ext3, ext4, btrfs and xfs file systems.