Table of Contents
Advertisement
v Methods that use backup and restore procedures will generally have the most
Replacing existing storage
To provide investment protection for IBM 7133 disk drives, the ESS supports reuse
of 7133 Model 020 and D40 drawers in 2105 Model 100 expansion enclosures.
Reformatting existing disk drive modules
To provide integrity-checking of data and to allow different operating systems to use
the ESS, IBM formats ESS 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 ESS. 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 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 Logical Volume Manager (LVM) uses a fixed-byte sector of 512 bytes.
When used in an ESS, the format is a fixed-byte sector of 524 bytes. The data
portion of the sector remains at 512 bytes. AS/400 headers use eight additional
bytes. A 2-byte sequence number and a 2-byte longitudinal redundancy check
(LRC) complete the extra bytes. The ESS LIC uses the sequence number and LRC.
The ESS does not transfer them to the host system. For a description of the new
format, see "524-byte sector format".
524-byte sector format
Most fixed-block disk architectures use a fixed-byte sector of 512 bytes. This
includes most UNIX systems, including AIX. When used in an ESS subsystem, the
format of a DDM has a fixed-byte sector of 524 bytes. The 524-byte sector format
enables the ESS subsystem to connect to a wide range of host systems and share
data between them.
The IBM AS/400 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 ESS. 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.
The sequence number is a modulo 64K value of the logical block address (LBA) of
this sector. It is an extra method of ensuring that you are accessing the correct
block.
The LRC, generated by the host adapter, is calculated on the 520 data bytes and
header bytes. The ESS uses the LRC as an error checking mechanism. The LRC
checks the data as it progresses from the host, through the ESS controller, into the
SSA adapter, to the array. See "UNIX systems" on page 81 for a detailed
description on data flow through the subsystem. The ESS also uses LRC as an
error checking mechanism as the ESS reads data from the array and passes it to
the host adapter. The ESS never transfers the sequence number and the LRC to
the host system.
80
ESS Introduction and Planning
impact on the system usage. They require that databases and file systems be in
quiescent states to ensure a valid snapshot of the data.
Advertisement
Table of Contents
