Re: RAW devices

<vasarpota_at_my-deja.com> wrote in message news:8m9sdg$9ga$1_at_nnrp1.deja.com...
> A few questions on the use of raw partitions.
>
> Do you guys use them? I know they can give you a performance boost if
> I/O is the bottleneck of the database and that data integrity is better
> if using them since always know that Oracle writes going to disk and
> not in OS cache but do you guys use them. I see that Oracle does not
> reccomend that you use them. Are raw devices very difficult to manage
> (e.g. backups, sizing/planning, etc.)? Are they worth the trouble?
>

The issue is, as you say, one of I/O. Raws come into their own for Online Redo Logs. If you mirror your redo logs (and you'd be mental not to) then poor ol' LGWR has to mnake the same entries in both (or all) members of each group -which could result in slower performance for the entire database unless you can somehow get the writes to the separate members to happen truly in parallel.

Most file systems do not support true asynchronous i/o, and accordingly it is quite often recommended that online redo logs should reside on raw devices (the lack of a file system means that true asynchronous i/o is almost a given).

However, they are actively discouraged for archived redo logs (there's actually an explicit 'prohibition' against putting archives on a raw device in the Oracle training materials). And they are also not much use for the data files.

And, I gather, most unix variants these days do a reasonable job of simulating asynchronous i/o (though not being a unix guru, I couldn't vouch for this for sure) -so inside Oracle these days its always a bit iffy whether to tall people to use raw devices even for online redo.

The problem as I understand it is that without a file system, you can't very easily manage your logs -there's nothing handy like 'mv' or 'rm' or 'cp' -you have to use 'dd' all the time, and I am constantly told by students on my courses that managing raw devices is (comparatively speaking) a pain in the butt.

I'd avoid 'em like the plague for anything other than redo logs, and I'd only bother using them for the logs if you can demonstrate that multiplexing your logs has caused significant performance degradation.

Regards
HJR
> Do you guys use cooked files to overcome the data integrity issue
> instead of raw partitions?
>
> Thanks for your help
>
> V-
>
>
>
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Received on Thu Aug 03 2000 - 00:00:00 CDT