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

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 Received on Fri Mar 31 2000 - 14:17:08 CST