Re: Disk I/O on Oracle redo logs

With RAID (RAID 1 or RAID 5) you will increase the number of IO necessary to write the same quantity of information. But without RAID you don't have any security for on line redo log files (unless you have multiplexed log files on 2 separate hard disk).
I think that the better way for on line redo log file is : - always separate physically it form other datafiles (don't mixed sequential IO and random IO).
- don't use RAID 5, but RAID 1 and stripping on 2 disk or more (RAID 1+0). You will increase trougthput.
- use raw device for redo log disk if possible. - If you need log archiving, separate archive log file from on line log file to prevent bottelneck on redo log disk. Normally, if you are not IO bound on redo log disk, archiving log don't reduce performances. If possible use 2 disk for on line redo log, put redo1 on disk 1, redo 2 on disk 2, redo 3 on disk 1, redo 4 on disk 2 etc. to prevent IO bottelneck when archiving (writing in current log file and reading the previous).

- tune log buffer and archive log buffer.
- use big redo log member to minimize the checkpoint number.
- if you are using sql*loader, use direct path and unrecoverrable option.

Tom Lewis a écrit dans le message <7ffs63$o7d$1_at_nnrp1.dejanews.com>...
>I have an Oracle 8.0.5 database where the datafiles resides on an 8 disk
RAID
>and the log files on a separate single disk. The application loads several
>million records into a number of tables (with no constraints) and then a
>PL/SQL cursor is used to copy the data into a relational model, via a
>select/insert process, to identify constraint violations. During large
data
>loads and the cursor select/insert process, disk I/O on the log files seems
>to be the performance-limiting factor.
>
>Would putting the log files on the RAID help performance, which is more
>important than resilience in this application? Also, does log file size
>affect performance (currently in “noarchivelog” mode to avoid further I/O
>problems but should start archiving in the future)?
>
>Any ideas gratefully received.
>
>
>--
>Tom Lewis
>
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Received on Tue Apr 20 1999 - 08:12:21 CDT