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338 DS8000 Series: Concepts and Architecture
Mirror data for higher availability and migration
The LUNs provided by the DS8000 appear to the LVM as physical SCSI disks.
Usually the process is to set up a mirror of the data on the old disks to the new LUNs, wait
until it is synchronized and split it at the cut over time. Some LVMs provide commands that
automate this process.
The biggest advantage of using the LVM for data migration is that the process can be totally
non-disruptive, as long as the operating system allows you to add and remove LUNs
dynamically. Due to the virtualization nature of LVM, it also allows for all kinds of
consolidation. Figure 16-4 shows the process.
Figure 16-4 Migration using LVM mirroring
The major disadvantage is that the LVM mirroring method requires a lot of system
administrator intervention and attention. Production data is manipulated while production is
running. Carelessness can lead to the outage that one wanted to avoid by selecting this
method.
Backup and restore
Every serious IT operation will have ways to back up and restore data. They can be used for
data migration. We list this method here because it shares the common advantages and
disadvantages with the methods discussed previously, although the tools will not always be
provided natively by the operating system.
All open system platforms and many applications provide native backup and restore
capabilities. They may not be very sophisticated sometimes, but they are often suitable in
smaller environments. In larger data centers it is customary to have a common backup
solution across all systems. Either can be used for data migration.
The backup and restore option allows for consolidation because the tools are usually aware
of the data structures they handle.
One significant difference to most of the other methods discussed here, is that it does not
require the source and target storage systems to be connected to the hosts at the same time.
Figure 16-5 on page 339 illustrates this method.
Initial Copy
Host
Update continuously
Host
Split mirror
Continue with new copy