Re: RE: Raid5 Vs Raid0+1 -- Raw Vs Solaris 9 Concurrent Direct IO

  • From: tim@xxxxxxxxxxxxx
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Wed, 25 Aug 2004 14:54:51 -0600 (MDT)

That is why RAID-0 striping is generally combined with RAID-1 mirroring, so 
that the load is distributed amongst more than just the single set of mirrored 
devices.
RAID-5 is simply a trade-off of performance for capacity, any way you cut it...

RAID-1 is redundancy with no compromise in performance.  Plain and simple...



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Subject: RE: Raid5 Vs Raid0+1 -- Raw Vs Solaris 9 Concurrent Direct IO
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From: "Nelson, Allan" <anelson@xxxxxxxxxxx>
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Raid 5 does get good read performance because for reads more disks get
in on the action.  3 in his example vs essentially 2 for the raid 0+1
stuff.

Allan

-----Original Message-----
=46rom: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of tim@xxxxxxxxxxxxx
Sent: Wednesday, August 25, 2004 2:16 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Raid5 Vs Raid0+1 -- Raw Vs Solaris 9 Concurrent Direct IO
UFS


Deen,
How can RAID-5 perform better than RAID-1 (especially 1+0) on reads=3F
That's a new one I've not heard before.  Oh, and writes=3F  Don't worry
about them -- we've got caching so it doesn't matter!

<rant>
Oh yes, the old "we've got so much cache it doesn't matter".  Don't
believe it:  cache has to be managed (possible source of contention) and
cache can be overwhelmed.  At best, cache smoothes out the spikes, but
it cannot help during a prolonged period of high activity.

I don't know why Sun thinks that there is a market for things like
=66ile-systems, but I've heard them waste hours trying to convince folks
to use their wonderful new UFS (yawn!).  At a large financial
institution last May, I participated in an Oracle-based benchmark with
=66our scenarios:  "regular" UFS (i.e. no direct I/O), UFS with direct
I/O, VxFS, and VxFS with "quick I/O" (now called ODM).  Then, for kicks,
the sys-admins and I added an "illegal" scenario -- "raw" logical
volumes -- to the mix.  The turd in the punch-bowl, the black sheep of
the storage family, the fifth option that none of the vendors wanted to
talk about.  We boiled each of the benchmark results down to a single
metric for relative comparison, with the first option (plain UFS) at a
score of 22, VxFS with 18, UFS with direct I/O also at 17-18, VxFS with
QIO/ODM at 12-13, and "raw" devices at 9.  Of course, because the use of
"raw" devices were "banned" from the competition (=3F), Veritas got their
sale.  Nev  ermind we were using VxVM for the logical volumes...  :-)

I count this as the best feat of marketing since Coke and Pepsi
convinced everyone that "soft drinks" are a part of daily life, adding
ump-teen layers of additional software to arrive a result that is
measurably less than simply removing the whole kit-and-kaboodle.
Paraphrasing the movie "Blazing Saddles":  "File-systems=3F  We don't need
no stinking file-systems...", but often that attitude is rather like
=66arting at the reception.

</rant  mode=3D"scuttles back into cave, pulls stone shut">

Hope this helps...

-Tim

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Date: Wed, 25 Aug 2004 14:17:30 -0400
=46rom: Deen Dayal <deen.dayal@xxxxxxxxxxxxxxx>
Subject: Raid5 Vs Raid0+1 -- Raw Vs Solaris 9 Concurrent Direct IO UFS
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We are planning to move our current database to new Hardware Sun 12k +
Hitachi SE 9970.=20

Our current database runs on Sun A5000 array with Raid0+1 on raw
devices. Sun engineer who is here at our site for implementation of
Hitachi SE9970 suggests that we should go Raid5 ( 3 + 1P ) in the parity
group as RAID5 gives better read performance than raid0+1 and any writes
are going to the cache any way, so we should not be worried about write
performance. There is 16GB cache on the Hitachi. Database is going to be
striped across 10 parity groups and each parity group consists of 4
physical disks.

Our application is about 60 to 70% reads most of the time, kind of a DSS
and for few batch jobs it is 90% write and 10% read. Database is not
that big just 200GB.

He also suggested us to use UFS instead of RAW as Solaris 9 has lot
improvements in UFS especially with Concurrent Direct I/O and can
perform better than RAW.

I am wondering anybody out there with real world experience with similar
Hardware can throw some light on these 2 topics. If anybody can point
any links or documents discussing these topics, highly appreciated.


Thanks
Deen

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