A technique involves determining, in redundant array of independent disks (RAID) stripes, source slices for restriping, and allocating, from a reserved capacity for file system check (FSCK), destination slices for restriping. The technique further involves performing restriping for the RAID stripes by copying data in the source slices into the destination slices. Accordingly, using the reserved capacity for FSCK as the destination slices for restriping may mitigate the influence on an available capacity of a mapper during restriping, thereby improving the performance of a storage system.