Re: Raw partitions vs. file system

From: S V <sv1_at_mindspring.com>
Date: 1997/10/28
Message-ID: <01bce3d4$43dd9be0$db5c0c26@sfinance3>#1/1

Billy Verreynne <vslabs_at_onwe.co.za> wrote in article

<01bce371$0619e060$f3040059_at_billyv.vslabs.co.za>...

> Jan Coekelberghs <jan.coekelberghs_at_ping.be> wrote in article
> <3458f827.1289460_at_news.belgium.eu.net>...
> > Suppose you work as a DBA in a company with +50 Oracle databases, all
> > of which use a file system.
> >
> > Now suppose you 'inherit' a database which uses raw partitions and you
> > want to get rid of them (eg. for manageability reasons). Is there a
> > way to determine if doing this will hit your performance? How? What
> > will (might) be the impact? Are there any other advantages in doing
> > so?
>
> AFAIK there is a very small performance increase when using raw
 partitions
> as OS i/o is bypassed. Oracle docs I've read suggest that raw partitions
 be
> used as the last resort when having i/o problems, so I think you'll be
 safe
> to move from raw to cooked files.

I have got quite significant perfomance boost when I went FROM filesystem TO raw logical volumes on AIX 4.2 platform. (I rutinely get 15 Mb/sec _sustained I/O rate on a full table scan - and this
is from a MTI RAID5 array sitting on a single Fast/Wide (not Ultra) SCSI controller).
And, in fact, Oracle perfomance tuning guide/tips for AIX platform does claim that Oracle performs significantly and consistently better when using raw devices than when using files. My own experience with raw logical volumes under AIX vs. files is all in favour of the former. Furthemore I found them to be easier to administer than filesystems. Just compare the time it takes to create 2G logical volume ( < 1 min) with a time it takes to create a filesystem the same size. Besides, it's quite easy to delete by mistake an Oracle file on a filesystem (we have seen quite a few folks here begging for help after doing just that). Not so for raw logical volumes.

Just my 2 c

Serge

>
> However, remember that if you're running OPS on a MMP/cluster-type
> platform, you have to use raw devices.
>
> regards,
> Billy
>
>
Received on Tue Oct 28 1997 - 00:00:00 CST