The slices depend on record size and sector size. For 4 data disks and default 128k record you have 32k per disk per record. With more disks, the proportion of

The slices depend on record size and sector size. For 4 data disks and default 128k record you have 32k per disk per record. With more disks, the proportion of a slice per disk decreases, not increases, and it's rounded up to the sector size, so there's usually some loss of space on larger parity schemas.