Re: 2 GB myth

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Wed, 24 Nov 2004 16:27:26 +1100
Message-ID: <41a41bc3$0$20857$afc38c87@news.optusnet.com.au>

Igor Laletin wrote:
> "Howard J. Rogers" <hjr_at_dizwell.com> wrote in message news:<41a2a9e6$0$20863$afc38c87_at_news.optusnet.com.au>...
>

>>Igor Laletin wrote:
>>
>>
>>>Not really. A number of datafiles doesn't have much impact on your
>>>workload. Also smaller datafiles usually don't mean much faster
>>>datafile recovery. True, you may get it restored on a disk a bit
>>>faster. The difference would be small though - current tape drives
>>>restore at 1G+/min.  After that you still need to go through all redo
>>>logs and it's the same for any datafile size.
>>
>>Have you used RMAN to backup a database. The number of data files is a 
>>heavy determinant of how well it can parallelise the operation. It can 
>>make a big difference.

>
>
> Well I was talking about recovery, not backup.

The two go together. You arrange your database one way because "it makes no difference to the speed of recovery" and you've just crippled my ability to backup in parallel properly. And guess which you do more often?

> Anyway, even with
> backups, most sites

I do wish people wouldn't talk this sort of talk. Morgan does plenty of it. You don't need to join the club.

Neither you nor I can be spokesmen for "most" sites on the global level. But on the grounds that most of the specific sites I have worked on backup and recovery strategies for actually backup to disk in the first instance, I am as qualified to say that you are wrong as you are to say the same of me.

> do them to the tapes. The tape drives are usually
> a bottleneck, not small number of datafiles. Say, you have four drives
> multiplexed by four (four processes feed data to one drive to keep it
> busy). You only need 16 datafiles to fully utilise tapes. Having 1K 2G
> datafiles instead of 100x20G won't make your backups faster.

Invariably not my experience.

You can't generalise past your own specific experience. So please don't.

HJR
>

>>HJR

>
>
> Igor
Received on Tue Nov 23 2004 - 23:27:26 CST