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The formatting tool dasdfmt provides options to format DASD devices
with different hard block sizes. With the described test we measured the impact
of different block sizes on performance.
The selected dasdfmt blocksize affects
the free disk space that a filesystem provides to the operating system.
This table lists free disk space on a 3390-9 (model 9 DASD) after formatting
the disk with ext2. |
|
dasdfmt blocksize |
free disk space |
|
512b
|
3.5G
|
|
1024b
|
4.7G
|
|
2048b
|
6G
|
|
4096b
|
6.8G
|
|
|
|
|
The following chart shows the iozone throughput while scaling the dasdfmt
blocksize (the throughput is displayed normalized per iozone mode).
|
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The dasdfmt blocksize of 4096b shows the best
results in iozone throughput and free disk space after formatting
the DASD device. Further tests showed that this statement
is independent to the request size issued by the application.
Even small application request sizes (e.g. 512b) showed the
best throughput with 4096b dasdfmt blocksize.
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- IBM eServer zSeries 990 2084-B16
- IBM TotalStorage Enterprise Storage Server 2105-800
- Linux 64bit, kernel 2.6.5
- LPAR with 4 CPUs and 256MB memory
- Single disk (ECKD); 1 process
- Benchmark Iozone 3.196, write, read, random; file size
700MB
- File system ext2
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