The disk format determines how much of the disk’s raw capacity can be used for data storage. Some disk formats cannot be combined in the same aggregate.
Most disks used in storage systems are block checksum disks (BCS disks).
The amount of space available for data depends on the bytes per sector (bps) of the disk:
- Disks that use 520 bps provide 512 bytes per sector for data. 8 bytes per sector are used for the checksum.
- Disks that use 512 bps use some sectors for data and others for checksums. For every 9 sectors, 1 sector is used for the checksum, and 8 sectors are available for data.
The disk formats by Data ONTAP disk type are as follows:
- FCAL and SAS BCS disks use 520 bps.
- ATA, SATA, and BSAS BCS disks use 512 bps.
- SSD BCS disks use 512 bps.
If you have an older storage system, it might have zoned checksum disks (ZCS disks). In ZCS disks, for every 64 (4,096 byte) blocks, one block is used for the checksum, and 63 blocks are available for data. There are rules about combining BCS disks and ZCS disks in the same aggregate.
