Re: ORACLE8 NT and RAID5

From: Jerry Gitomer <jgitomer_at_hbsrx.com>
Date: Fri, 23 Jul 1999 12:41:48 -0400
Message-ID: <7na609$jf3$1@autumn.news.rcn.net>

Rule #1:  Do not use software RAID 5 on NT.
Rule #2:  Do not put redo logs on RAID 5
Rule #3:  RAID 5 is fine for data which is "write once, read

many" but should not be used if your data is "write once, read less than 4 times"

Source of rules: My getting burned when I inherited RAID 5 (Once on NT and once on AIX).
By the way the 4 times in my Rule #3 is arbitrary and capricious -- but then us DBAs get that way :-)

regards
Jerry Gitomer

zen_nj_at_my-deja.com wrote in message
<7n9s86$mnq$1_at_nnrp1.deja.com>...
>Hi
>
>Does anyone have general guideline/practice on the best way
>to configure RAID for database devices ?
>
>Specifically, from articles I read on RAID, it seems to be
>saying:
>
>1. if your database is OLTP and update intensive, you want to
stay away
> from RAID5 (I assume due to the additional write to parity
disk).
>2. Likewise, I have read conflicting suggestions where someone
would
> recommend RAID5 since it's great for random access (read) but
> then someone else would not since when there is disk failure,
RAID5
> read performance would degrade greatly (having to generate
missing
> disk data from parity and stuff).
>3. I also read something that if your database is DSS and makes
> extensive use of sort areas and temporary tables, then
RAID10 (0+1)
> is the best options. And if this storage are transient (only
valid
> during execution of a sort/join), then you could just use
RAID-0
> striping.
>
>Does this mean that for tempdb, we could just use RAID-0
configuration
>(or maybe just by-pass RAID altogether and set it up on a file
>system) ?
>
>And what about the log devices ? Since we need to ensure it's
>recoverability, we could either use RAID1 or RAID5 or RAID10.
>If we have the extra disk capacity, would RAID1 be the way to
>go ? Or would RAID10 be actually better ?
>
>For data that are predominantly DSS (but do get updated as a
nightly
>batch), should we use RAID5 then ? Or if we do have extra
disks,
>just use RAID1 as well ? Or is there a better configuration ?
>
>For data that will be updated somewhat frequently and need to be
>redundant/mirrored, it seems to be a choice between RAID1 and
>RAID10. (I was told RAID1 write performance isn't too bad,
especially
>for Clarion RAID and using write cache).
>
>So if we have the extra disk capacity, it sounds like we could
just
>configure pretty much everything for RAID1 (with exception of
the
>tempdb). Is RAID10 a better option than RAID1 only if you care
>about expense (since RAID1 requires more disk) or does it
actually
>offer better performance ?
>Does RAID5 offer better performance than RAID1 or RAID10 in any
>area ?
>
>If someone can help dispell any misunderstanding/myth on this,
it
>would help us greatly. Thanks
>
>Zen
>
>
>
>In article <01bed1d4$5d8d8420$ce1e1dac_at_ut9811252159>,
> "Kaboel Karso" <karso_at_kpn.com> wrote:
>> hi,
>>
>> RAID0 = striping
>> RAID1 = mirroring
>> RAID2 = duplexing
>> RAID5 = striping with calculation of the parity bit placed on
all the
>disks
>> participating in the raid volume using these in a round robin
fashion
>> RAID10 = striping & mirroring
>>
>> Saying that, you should investigate what the different raid
levels is
>> actually doiing. For performance reasons RAID0 is preferrable.
As for
>> reliability, you must have some sort of protection. The best
scenario
>is
>> using RAID10 (RAID 1+0). btw, there is a difference between
RAID 0+1
>and
>> RAID 1+0 , not performance wise but in case of a disaster.
>>
>> Imo, the next best scenario is to use RAID5 for the datafiles
and
>place all
>> other files causing sequential writes e.g the redo logfiles,
on a non
>> raided disk. The redolog files preferrably mirrored by Oracle.
>>
>> I found some whitepapers on this topic on the SUN website a
while ago.
>> Maybe they're still available.
>>
>> Kaboel
>>
>> dcoan_at_aegonusa.com schreef in artikel
<7mo0dg$obe$1_at_nnrp1.deja.com>...
>> > In article <7mnmu1$k2i$1_at_nnrp1.deja.com>,
>> > drfuller1_at_my-deja.com wrote:
>> > > We are currently configuring a new NT server for our
Oracle8
>database
>> > > and I would like to know the pros or cons of using raid5
ot if
>anyone
>> > > has a better recommendation, it would be appreciated.
>> > >
>> > > Thanks,
>> > > Don
>> > >
>> > > Sent via Deja.com http://www.deja.com/
>> > > Share what you know. Learn what you don't.
>> > >
>> >
>> > A subject near and dear to my heart...... We are Oracle 7 nd
8 on NT
>> > also.
>> >
>> > All raids give about the same level of fault tolerance.
>> >
>> > We recently had the opportunity to do some performance
comparing of
>RAID
>> > levels in a real world environment using both compaq and EMC
dasd.
>Here
>> > are the results:
>> >
>> > Raid Level - Cycle times
>> > Raid 5 (EMC RAID S) - 23 hours
>> > Raid 1 (EMC) - @12 hours
>> > RAID 10 (0+1) (Compaq) - @11 hours
>> >
>> > We never did RAID 10 on EMC because of the minimum stripping
size on
>> > EMC. However, I still think that would have given us the
best
>> > performance.
>> >
>> > We also have a Sybase serrver where performance of a query
went from
>1
>> > hour to about 9 minutes by just going from RAID 5 to RAID
10.
>> > (SERIOUSLY!!)
>> >
>> > Of couse the EMC DASD costs about 10-20 times the compaq and
has
>@5GB of
>> > cache, so we were surprised to see such a giant timing
difference,
>but
>> > it was there and proven several several several times using
several
>> > servers and Oracle configs.
>> >
>> > DASD vendors and people will give you the old 'But
everything is
>comming
>> > from disk Cache' and 'You don't understand how OUR Raid 5
works' and
>the
>> > ever famous 'let me show you this white paper' arguments.
DON'T FALL
>FOR
>> > IT!!!!!!! Simply, tell them to prove it on your DB in your
shop.
>> > Perhaps in your envinment with your DB (ie a DSS db) the
performance
>hit
>> > will not be too bad.
>> >
>> > In General:
>> > Raid 5 - SLOW, least expensive
>> > RAID 1 - Fast, More expensive
>> > RAID 0+1 - Fastest, Same expence as RAID 1
>> >
>> > Other RAIDs - not really worth mentioning. Avoid them.
>> >
>> > On a RAID 5 array, performance will degrade more than on
other RAIDs
>if
>> > a drive fails.
>> >
>> > Bottom Line Recommendations:
>> > - More spindles are better.
>> > - Stripe the data across spindles.
>> > - If you can afford it go RAID 10 (0+1) DO IT!!!
>> > - Aviod OS level striping - Do hardware level
>> > - Raid 1 is an ok alternative, but requires more support as
far as
>> > placement is concerned to get the performance.
>> > - Only use RAID 5 when ..... Well - Just don't unless you
have NO
>other
>> > choice and you prove the performance is acceptable and you
can live
>with
>> > it forever. Remember - The choice you make today becomes
tomorrows
>> > 'thats we way we have always done it' and it is used
everywhere.
>> >
>> > WOW - How high can I stack this soapbox? :-) Good luck.
>> >
>> > Doug Coan
>> > Senior Client Server System Integrator
>> > AEGON USA
>> > dcoan_at_aegonusa.com
>> >
>> >
>> > Sent via Deja.com http://www.deja.com/
>> > Share what you know. Learn what you don't.
>> >
>>
>
>
>Sent via Deja.com http://www.deja.com/
>Share what you know. Learn what you don't.
Received on Fri Jul 23 1999 - 11:41:48 CDT