From: Chris Bryant (Chris.Bryant@DTAG.Com)
Date: Tue Jul 29 2003 - 13:56:23 EDT
Thanks to Alan Rollow and HP Tru64 Gold support team for their responses.
Alan Rollow:
I tried a test on V4.0G and was able to read 8 MB in
a single I/O from /dev/zero without any hint of a
problem. At larger than 8 MB, dd(1) to misreport
the transfer, but wrote the expected amount of data.
Individual disk drivers may have their own limits, but
these may be indicated in the DDR database entry for
the device class or type. I've regularly used 1 MB
I/Os to SCSI tapes without any apparent trouble.
Really large I/Os can tie up a fair amount of memory,
the memory for the buffer has to be locked so that it
can't page out. Many such buffers could put undue
stress on the virtual memory system.
Gold support had me check chvol -l special domain and on 5.x system it came
back with max of 2048 block = 1048576 or 1 Meg.
Thanks again,
Chris Bryant
-----Original Message-----
From: Chris Bryant
Sent: Friday, July 25, 2003 10:30 AM
To: Tru64 Unix (tru64-unix-managers@ornl.gov)
Subject: Max I/O packet size
Admins,
This is a question that one of our DBA's has"
Could you please find out the MAX I/O size that OS can read ?
In oracle it is set at 8 block (64K). We are wondering maybe we can set this
parameter (db_file_multiblock_read_count) higher to improve the performance.
TIA,
Chris Bryant
UNIX Administrator
Dollar Thrifty Automotive Group
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