To provide integrity-checking of data and to allow different operating systems to use the storage unit, IBM formats storage unit disks to a 524-byte sector.
The 524-byte sector replaces the traditional 512-byte sector of fixed-block architecture disk drive modules (DDMs). The 524-byte sector format requires that you reformat all disks that you are migrating to the storage unit. Because reformatting will erase any data that is already contained on the drives, you must back up the data to some form of temporary storage.
You can use the disk drive module (DDM) for either direct migration of data or as temporary storage while the existing drives are moved. If this is not possible, use a removable media device such as a tape drive to temporarily store the data while you reformat the drives.
The AIX LVM uses a fixed-byte sector of 512-bytes. When used in an storage unit, the format is a fixed-byte sector of 524-bytes. The data portion of the sector remains at 512-bytes. AS/400 and iSeries headers use eight additional bytes. A 2-byte sequence number and a 2-byte longitudinal redundancy check (LRC) complete the extra bytes. The storage unit LIC uses the sequence number and LRC. The storage unit does not transfer them to the host system.
Most fixed-block disk architectures use a fixed-byte sector of 512-bytes. This includes most UNIX systems, including AIX. When used in an storage unit, the format of a DDM has a fixedbyte sector of 524-bytes. The 524-byte sector format enables the storage unit to connect to a wide range of host systems and share data between them.
The 524-byte sector on the DDM is independent of the sector size exposed to the host for a given device type emulation. Most LUNs for open-systems hosts are exposed with a 512-byte sector.
The IBM AS/400 and iSeries host systems use eight bytes at the start of the sector. UNIX host systems do not use these eight bytes when you attach them to the storage unit. The data portion of the sector remains at 512-bytes for all host systems. A 2-byte sequence number and a 2-byte LRC increase the size of the sector to 524-bytes.