Internal Magnetic Media 337
Internal Magnetic Media
models, there are two buses per tower. Therefore, tower level mirroring would be used in
place of bus-level mirroring because a tower comprises a single point of failure. When a
disk-related mirrored component fails, the system remains available.
Integrated Hardware Disk Compression
Data is dynamically compressed or uncompressed by the DASD controller as data is written
to and read from disk. Disk compression has no affect on the main CPU utilization since
compression is performed by the DASD controller input/output processor (IOP).
Support for Integrated Hardware Disk Compression is provided by DASD controllers #2741,
#2748, #4748/#9748, #6533, and CCIN 671A MFIOP. Compression is limited to user ASPs.
The compression ratio results of DASD varies. The compression ratio achieved and the
impact on DASD performance depends on the data and how it is accessed.
Internal Tape, CD-ROM, and DVD-RAM
The following table shows which tape units are supported in the 250, 270, and 8xx systems,
expansion towers, and migration towers.
Internal Tape Media System and Expansion Unit Supported
Fea-
ture
Size
250 270 820
830/
840
#5077
#5072/
#5073
#5074/
#5079 #503x
#5065/
#5066
#1349 1.2 GB ¼” S
#1350 2.5 GB ¼” S
#1355 13 GB ¼” S
#1360 7 GB 8mm S
#1379 1.2 GB ¼” SS
#1380 2.5 GB ¼” SS
#4425 CD-ROM N N M
#4430 DVD-RAM N N
#4482 4 GB ¼” NNM
#4483 16 GB ¼” NNM
#4486 25 GB ¼” NNM
#4487 50 GB ¼” NN
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