Re: Does RAID 5 contradict and minimize the benefit of OFA on NT?

Howdy, sorry for barging in, but may I ask a few questions?

1. I take it we should not put the Oracle db files on a RAID5 volume, correct?
2. The redo log file should be on a separate physical disk from the db & also not on a RAID5 volume, correct? I would choose a RAID1 volume for the redo logs.
3. To reduce the possibility of disk contention, the archive log files should be separate from both the db & the active redo log files. To keep the number of disks down to a minimum, under what circumstances can we keep the archive log files on the same disk as the active log files (assuming we have RAID1 for fault tolerance)?
4. How does one size the redo log files? When do we use, say, 3 10MB files vs. 3 100MB files (with ARCHIVELOG on)?

Thank you.

Sybrand Bakker wrote:
>
> david spaisman <david.spaisman_at_compaq.com> wrote in message
> news:8c303v$6hm$1_at_mailint03.im.hou.compaq.com...
> > Sybrand:
> >
> > Thanks for quick and helpful reply.
> >
> > I had thought that mirroring the redo logs on separate disks would avoid
> > problems if one memeber of a redo log is corrupted. How would I avoid this
> > problem : in my configuration, I beleive I should place the redo log
> > memebers on disk 1, 4 and disk5.
> >
> > Your reply on not putting critical file on RAID 5 devices would lead me
 to
> > have in my configuration(not the actual drive letters to be used):
> >
> > Drive a) if this is to be raid 5, I should keep my system tablespace on
 disk
> > d or disk e. If I have disk a set up for RAId 1 I would be ok?
> >
> > If disk a,b c, d and e or disk b,c ,d,e are raid 5 enabled, where do I
> > spread out the control files-- on which drives?
> >
> > Thanks again for the very helpful response. Unfortunately, translating
 dutch
> > would be an eternity for me.
> >
> > David Spaisman
> >
> >
> > Sybrand Bakker wrote in message
> > <954531184.21961.0.pluto.d4ee154e_at_news.demon.nl>...
> > >Answers embedded
> > >david spaisman <david.spaisman_at_compaq.com> wrote in message
> > >news:8c2sr8$55r$1_at_mailint03.im.hou.compaq.com...
> > >> Hello:
> > >>
> > >> I am working on Oracle 8.0.5 application on NT 4.0. We are in the
 process
 of
> > >> setting up a user acceptance server and a development server and have
 the
> > >> luxury of having as many disk servers as needed on each respective
> > >> server(within reason).
> > >>
> > >> I am thinking of going with a configuration of drives consisting of
 the
> > >> following:
> > >>
> > >> a) Oracle executibles, redo log group members, control file, system
> > >> tablespace
> > >> b) data files, user files, control file, redo log members
> > >> c) index files, control file, redo log members
> > >> d) rollback segments, export files, backup files
> > >> e) archive log files.
> > >>
> > >> Hopefully this configuration will be with physically separate drives
 and
> > >> more than one controller If these are logically partitioned drives, I
> > >> believe it will still depend on how many physical drives and
 controllers
> > >> are involved. THanks.
> > >>
> > >> David Spaisman
> > >>
> > >>
> > >> However, I have been told that RAID 5 will reduce or contradict the
> > >> ebenfits purportedly gained from the multiple disk drive/OFA
 configuration.
> > >>
> > >> 1) Has any one found this to be true?
> > >>
> > >Yes, basically you really can't distribute your data as all your logical
> > >volumes are spread out on several physical volumes. If you dedicate 1
 RAID
> > >disk to indexes, your indexes will still show everywhere.
> > >
> > >
> > >> 2) Will the benefit of RAID 5 -- faster reads versus slower writes --
 for
 a
> > >> transactonal database still apply?
> > >>
> > >No, RAID 5 will hurt performance and cause bottlenecks especially for
 files
> > >being sequentially written only, like redo log files. Your setup with
> > >redolog files on disks with tablespaces is likely to result in
 performance
> > >hits.
> > >> 3) Has any one seen Oracle position on the value OFA versus the
 benefit
 of
> > >> RAID 5?
> > >>
> > >No, though the consensus in this group is : use a combination of RAID0+1
 and
> > >RAID-5, do NOT place critical files on RAID-5 devices.
> > >A recent article in the Dutch Oracle Magazine Optimize summarizes as
> > >follows.
> > >If your database has less than 50 users and/or less than 250 OLTP
> > >transactions per minute there should be no objection against RAID5. If
 one
> > >of these parameters is exceeded and/or you are running more databases on
 one
> > >server, you should consider using other disks.
> > >The article discusses heavy OLTP environments, I'm not sure whether you
 need
> > >that, and it will be a hell of a lot of work to translate from Dutch to
> > >English.
> > >
> > >Hth,
> > >
> > >Sybrand Bakker, Oracle DBA
> > >
> > >> 4) Any other information concerning this situation will be greatly
> > >> appreciated.
> > >>
> > >> Thanks.
> > >>
> > >> David Spaisman
> > >>
> > >>
> > >>
> > >>
> > >
> > >
> >
> >
>
> With 5 disks, I would probably make sure two are non-Raid or RAID0+1.
> According to the article RAID5 should get
> software
> exports
> hot backup
> archive logs
> The rest is on RAID0+1 or RAID10 or non-RAID
>
> With respect to redo log I have always believed you should use either hw
> mirroring (RAID) or sw mirroring (multiple members), but not BOTH. It won't
> help you either, if one of the disks of that stripe set goes down, the
> database will probably detect inconsistencies and crash.
> In your config I wouldn't definitely not use 3 log file members, only 2.
> Given the time of the day here (22:16) I would probably not endeavour to
> come up with a different config.
>
> Hth,
>
> Sybrand Bakker, Oracle DBA
 

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