IBM Tape Solutions for Storage Area Networks and FICON

156 IBM Tape Solutions for Storage Area Networks and FICON

LINK=(D2,D3),

UNITADD=((00,16)),

UNIT=3590

IODEVICE ADDRESS=(7040,016),

UNITADD=0,CUNUMBR=(0650),

STADET=Y,UNIT=3590

6.3.5 Performance

FICON channels have a peak data rate of 100 MB/sec compared to a peak data rate for

ESCON channels of 17 MB/sec. These figures discuss the performance of the 3590-A60

rather than earlier products. Under many circumstances, the data transfer speed of the

3590-A60 is double that of the predecessor 3590-A50 controller.

All measurements in this section were conducted in a point-to-point configuration, and run on

an IBM G6 processor. Drives were attached to the 3590-A60 using UltraSCSI interfaces.

FICON attachments used longwave adapters, although the performance of shortwave

adapters at equal distances should be the same. Two programs were used that differed

primarily in the access method they employed to write or read data: either QSAM or EXCP.

For large block sizes or highly compressible data, the higher interface speed with Fibre

Channel drive attachment to the 3590-A60 can increase throughput. This occurs when the

drive can deliver data at a rate faster than the 40 MB/sec allowed by an UltraSCSI interface.

Figure 6-12 shows that the maximum native data rate of 14 MB/sec for a 3590E drive is

achieved for a 16 KB block size when FICON-attached. ESCON attachment does not permit

the maximum data rate to be achieved until block size is roughly 64 KB. Compaction was

turned off for these measurements to see the native data rate without any compaction effects.

Note: Some of these measurements use tape block sizes in excess of 32 KB. Before

OS/390 2.10, you can get block sizes up to 32 KB using QSAM, and up to 64 KB using

EXCP. DFSMSdss™ typically uses block sizes greater than 32 KB. With OS/390 2.10,

you may use block sizes up to 2 GB, subject to device limitations. OS/390 large block

size support has a number of implications which are described in DFSMS Release 10

Technical Update, SG24-6120.

Chapter 6. FICON attachment of IBM tapes 157

Figure 6-12 Single 3590E drive, FICON, and ESCON attachment

DFSMShsm™ uses a 16 KB block size for incremental backup and for migration tapes.

QSAM block sizes are limited to 32 KB. In each case, FICON attachment provides greater

throughput at the drive level.

Figure 6-13 again shows measurements for a single drive. In this case, the data used for the

measurements is compressible at a compression ratio of three to one (3:1), a ratio that is

typical of much production data. The chart shows that a 3590E out-performs a 3590B for

higher block sizes. However, the key point in the chart is that a single 3590 drive with data

compressing at 3:1 can exceed ESCON throughput at a block size as low as 16 KB.

Figure 6-13 Single 3590 drive with 3:1 compression

The 3590E at a 128 KB block size writes data at about double the sustained capacity of an

ESCON channel.

4K 8K 16K 32K 64K 128K

BLOCK SIZE

0

5

10

15

14

DATA RATE (MB/S)

ESCON FICON

Compaction off

3590 E ESCON vs. FICON

16K 32K 64K 128K

BLOCK SIZE

0

10

20

30

40

32

DATA RATE (MB/S)

3590 B 3590 E

ONE DRIVE WRITING 3:1