Chapter 2. System structure and design 71
Draft Document for Review April 7, 2004 6:15 pm 6947ch02.fm
Remember that logical partitions are currently limited to a maximum size of 128 GB of
storage.
2.2.11 LPAR Dynamic Storage Reconfiguration (DSR)
Dynamic Storage Reconfiguration (DSR) on z990 servers allows an operating system running
in a logical partition to add non-disruptively its reserved storage amount to its configuration, if
any unused storage exists. This unused storage can be obtained when another logical
partition releases some storage, or when a concurrent memory upgrade takes place.
With enhanced DSR, the unused storage does not have to be continuous.
When an operating system running in a logical partition assigns a storage increment to its
configuration, PR/SM will check if there are any free storage increments and will dynamically
bring the storage online.
PR/SM will dynamically take offline a storage increment and will make it available to other
partitions when an operating system running in a logical partition releases a storage
increment.
2.2.12 I/O subsystem
All models have one I/O subsystem. The I/O subsystem should be considered as the physical
entity that encompasses all control functions and all connections to all devices.
The z990 I/O subsystem provides great flexibility and high availability and performance,
allowing:
򐂰High bandwidth
The z990 I/O subsystem can handle up to 96 GB/sec; this is four times the z900 server’s
bandwidth. Individual channels can have up to 2 Gb/sec data rates.
򐂰Wide connectivity
A z990 server can be connected to an extensive range of interfaces, using protocols su ch
as Fibre Channel Protocol (FCP) for Small Computer System Interface (SCSI), Gigabit
Ethernet (GbE), Fast Ethernet (FENET), 1000Base-T Ethernet, and High Speed Token
Ring, along with FICON, ESCON, and coupling link channels.
򐂰Concurrent channel upgrades
It is possible to concurrently add channels to a z990 server provided there are unused
channel positions in an I/O cage. Additional I/O cages can be previously installed on an
initial configuration via Plan Ahead, to provide greater capacity for concurrent upgrades.
This capability may help eliminate an outage to upgrade the channel configuration. For
more information about concurrent channel upgrades, see “CUoD for I/O” on page193.
򐂰Dynamic I/O reconfiguration
Dynamic I/O reconfiguration enhances system availability by supporting the dynamic
addition, removal, or modification of channel paths, control units, I/O devices, and I/O
configuration definitions to both hardware and software (if it has this support), without
requiring a planned outage.
򐂰ESCON port sparing and upgrading
The ESCON 16-port I/O card includes one unused port dedicated for sparing in the event
of a port failure on that card. Other unused ports are available for growth of ESCON
channels without requiring new hardware, enabling concurrent upgrades via Licensed
Internal Code.