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MQSeries.net Forum Index » IBM MQ Installation/Configuration Support » Archive log block size

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blowbeat
PostPosted: Tue Dec 03, 2002 1:14 am    Post subject: Archive log block size Reply with quote

Apprentice

Joined: 02 Apr 2002
Posts: 49
Hi,

For those who still believe in 'tuning'...

The default blocksize for Archive logs is 20480 (5*4096).
No doubt chosen by IBM because this represents optimum blocking on a 3380 disk (since lrecl=4096). But since 3390's have a larger track size, an optimum blocksize would be 24576(6*4096).
Saves about 1/6 of the allocated archive log....

Cheers, Jan.
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bob_buxton
PostPosted: Tue Dec 03, 2002 7:19 am    Post subject: Reply with quote

Master

Joined: 23 Aug 2001
Posts: 266
Location: England
The system setup up guide does already reccomend setting blocksize 24576 for 3390 devices and 28672 for tapes.
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Bob Buxton
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blowbeat
PostPosted: Tue Dec 03, 2002 7:32 am    Post subject: Reply with quote

Apprentice

Joined: 02 Apr 2002
Posts: 49
Yes, it does. I just found out the hard way. Some set this to 28672.
So the amount of DASD used is twice what it should be with 24576.
It seems as of 53 the default is 28672. Does the CSQ6ARVP have the intelligence to lower it to 24576 when the UNIT is not TAPE ?

Jan.
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bob_buxton
PostPosted: Tue Dec 03, 2002 7:50 am    Post subject: Reply with quote

Master

Joined: 23 Aug 2001
Posts: 266
Location: England
No intelligence!

The default unit is TAPE so with default blocksize matches default unit,
If you change one you should change the other.
The default was changed in 5.2 but unfortunately the book wasn't updated.
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Bob Buxton
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