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Only data that has changed during the outage needs to be resynchronized between
the copies, a simple operation that greatly reduces resynchronization time.
Note: The ESS supports this function on System/390 MVS operating systems only.
If you need to change the default setting for an outage, you can do so through the
ESS Copy Services Web interface. The Copy Services servers must be identified
and set up by IBM service personnel prior to your using the ESS Copy Services
Web interface.
See the IBM Enterprise Storage Server Web Interface User's Guide for the
procedures for changing the XRC time-out from the ESS Copy Services Web
interface.
Concurrent Copy
The ESS supports the Concurrent Copy feature on System/390 hosts. Concurrent
Copy, like FlashCopy, creates point-in-time copies of volumes. However, Concurrent
Copy can also copy data sets from a source volume. It can copy the data to tape,
an optical library or to another DASD device. Data systems like the IBM DB2
product, can also initiate Concurrent Copy.
Multiple allegiance
The Multiple Allegiance feature allows the ESS to accept an input/output (I/O)
request from each channel path group for a unit address. The request can be
concurrent with other I/O requests. The ESS queues requests and then initiates
them. This allows you to have multiple access to a shared volume (logical device)
without affecting performance.
Using the Multiple Allegiance feature can improve ESS throughput and
performance.
Parallel Access Volume
The Parallel Access Volume (PAV) feature allows you to access a CKD volume on
an ESS in parallel. With PAV, you assign a base address to a CKD logical device.
You can use any of the 256 available addresses as the base device address. You
then configure alias addresses for the CKD logical device.
You can then dynamically reassign any configured alias address from one CKD
logical device to another CKD logical device. Address types are:
v Base address
v Alias address
See the IBM Enterprise Storage Server User's Guide for more information on using
PAV.
Descriptions and comparisons of the IBM Enterprise Storage Server
models
This section describes the ESS models and features.
20
ESS Introduction and Planning
The base address is the unique unit address of a volume. The ESS associates
storage space with this address.
You can assign several alias addresses to the base address. The ESS runs I/O
operations to the alias address against the base address.
With PAV, a single System/390 can simultaneously process multiple I/O
operations to the same logical volume. This can reduce volume contention.
®
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