DASD controllers, such as the IBM 3990 and 3880's.
Line printers, such as the IBM 3900
Tape drives such as the IBM 3480, and 3490
Communication controllers, such as the IBM 3745 unit
SNA display controllers such as the 3174
S/390 DASD Attachment
Direct channel connection of the IBM S/390 Integrated Server to S/390 ESCON
DASD devices is supported.The S/390 Serial Channel Adapter must be used
for this function.
Restrictions when using the S/390 ESCON Channel Adapter
Only specific IBM devices have been tested.Because of timing
considerations, non-IBM implementations of these devices may not
DASD attachment is only supported on ESCON Serial Channel adapters.
A maximum of two ESCON adapters is supported.
Only ESCON channel functions are supported. ESCON to Parallel
converter and CTC function is not supported, however a S/390 Serial
Channel adapter can connect to another S/390 system where the CTC
“load” is in that system's channel.
Multi-path is not supported (two channels to same device controller).
S/370, S/390 DASD migration to internal disk storage
In some cases, migration of existing S/370 or S/390 DASD to the S/390
Integrated Server's internal emulated DASD is favorable.Standard
Dump/Restore programs should be used to accomplish this.
If the source DASD is ESCON attached to the IBM S/390 Integrated Server
then a program such as DFDSS can be used to copy the data from the
ESCON attached DASD to the emulated DASD on the IBM S/390 Integrated
Server without the intermediate step of dumping the DASD volume to tape.
If the source DASD has a prallel attachment to another S/370 or S/390 system,
then the DASD must be first dumped to tape, then restored to the emulated
DASD on the IBM S/390 Integrated Server using standard dump/restore
The IBM S/390 Integrated Server has sixteen internal Hot/Swap drive bays,
each of which can accommodate an 18GB disk drive.The normal configuration
will include up to sixteen 18GB disk drives providing approximately 255GB of
useable disk capacity in a RAID 5 configuration.To provide enough read/write
access mechanisms to maintain good performance, at least five active drives
are recommended to be configured for each IBM S/390 Integrated Server.
Using less than five active drives may seriously limit the disk I/O performance
of the system.
Additionally, you may be able to split your workload across multiple IBM S/390
Integrated Servers.Analysis is needed to determine if workloads and data can
be logically divided between an existing system and the IBM S/390 Integrated
Chapter 7.Planning Guide23

Server or between two IBM S/390 Integrated Servers.The main reason for
splitting workload is to achieve better performance when accessing data.
Disk I/O Performance and Caching
The disk I/O rate (measured in S/390 I/O operations per second) which the IBM
S/390 Integrated Server is able to sustain will vary greatly from system to system,
depending on workload characteristics and system configuration.Some workloads
may saturate the I/O subsystem at an average of 100 I/Os per second, while other
workloads can successfully run with peaks up to 400 I/Os per second.If the
expected S/390 disk I/O rate falls between 100 and 400 I/Os per second, check
with your certified reseller for additional guidance.
In general, the more I/O intensive the workload, the higher potential for bottlenecks.
using data caching techniques, I/O bottlenecks can be reduced.
The IBM S/390 Integrated Server environment throughput can be improved through
I/O caching.Caching writes in either of the methods described below may improve
the ability to drive higher I/O rates through the IBM S/390 Integrated Server
depending on the read/write ratio.However, because the standard integrated
controller's cache is not backed up with a battery, certain system failures can cause
data integrity exposures that can be minimized by using an optional IBF.See
“Power Management” on page9.
Software caching using the IOSP memory to store I/Os before writing to the hard
disk is enabled using the LAZY WRITE option of OS/2.A specific amount of
memory is reserved for caching use.This value is defined in the CONFIG.SYS file.
a High Performance File
System (HPFS), use the CACHE command to enable
and disable lazy-writes.(The default is on.)For
a FAT file system use the
DISKCACHE command.
When a write operation is issued from a program, the I/O is written to the cache
and the issuing program is informed that the write I/O is complete before the data is
actually written to the hard disk.Data integrity exposure exists if there is a power
failure (without an IBF), an OS/2 failure that cannot be recovered with a soft boot,
or some hardware caused failure.
Another form of caching is to make use of S/390 Expanded Storage to allow the
S/390 operating system to keep more data in storage and avoid doing I/O
operations. IOSP memory can be used to emulate S/390 Expanded Storage.This
may offer a significant overall performance improvement for systems and
applications which can take advantage of Expanded Storage.This is available only
on the VM/ESA and OS/390 operating systems.If your VSE/ESA operating system
is executing natively, third party software (Opti-Cache) from Barnard Softare Inc. is
available to provide the advantages of S/390 expanded storage.
As with all systems, the performance benefits and applicability of caching is
dependent on the operating system and its workload characteristics.
24 S/390 Integrated Server
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