Log file Raid 1 VS Raid5 on EMC symmetrix DMX

Hi! Ever since I worked with sql server I have been placing sql log files on
Raid 1, which is the recomendation I read everywhere (from books, internet
etc).
Now, we are going to use EMC symmetrix DMX and folks here want to save some
money by configuring RAID 5 for both datafile and log file. Their
justification is, EMC DMX is totally different architecture and its fast, so
there won't be much difference between Raid5 and Raid1 for Sql server.
Is this true? Is anyone using EMC for Sql log file with Raid 5
configuration? Is there any whitepaper or artical that specifically talks
Sql log file on EMC.
I appreciate your help.my inclination is not to believe it. I have encountered
situations where high-end storage systems have absolutely
horrible performance because some one advise RAID5 without
actually running tests to prove it
i strongly recommend that you get IOmeter, originally
developed at Intel.
http://sourceforge.net/projects/iometer/
test the RAID configuration with the full size of the
expect data and log file using random read/writes
i would also advise testing to see if a large cache on the
storage controller has any value over a small cache,
>--Original Message--
>Hi! Ever since I worked with sql server I have been
placing sql log files on
>Raid 1, which is the recomendation I read everywhere
(from books, internet
>etc).
>Now, we are going to use EMC symmetrix DMX and folks here
want to save some
>money by configuring RAID 5 for both datafile and log
file. Their
>justification is, EMC DMX is totally different
architecture and its fast, so
>there won't be much difference between Raid5 and Raid1
for Sql server.
>Is this true? Is anyone using EMC for Sql log file with
Raid 5
>configuration? Is there any whitepaper or artical that
specifically talks
>Sql log file on EMC.
>I appreciate your help.
>
>.
>|||Do you mean they want to put the log file and the data on the same Raid 5 or
just 2 different raid 5's. If it's the first then I would make them prove
to you that it can handle the load at your peak transaction rates and not to
forget during backups. If you have a low enough transaction rate and a fast
enough disk subsystem you may not notice but if your going to an EMC then
you most likely have a fair amount of transactions. If they will be on 2
different array's and nothing else is on the array with the logs that is a
different story. But Raid 5 is still worse on writes than a Raid 1 and
won't save any money since a Raid 1 is usually smaller than a similiar Raid
5.
--
Andrew J. Kelly
SQL Server MVP
"james" <kush@.brandes.com> wrote in message
news:%23nS1c2fUDHA.3308@.tk2msftngp13.phx.gbl...
> Hi! Ever since I worked with sql server I have been placing sql log files
on
> Raid 1, which is the recomendation I read everywhere (from books, internet
> etc).
> Now, we are going to use EMC symmetrix DMX and folks here want to save
some
> money by configuring RAID 5 for both datafile and log file. Their
> justification is, EMC DMX is totally different architecture and its fast,
so
> there won't be much difference between Raid5 and Raid1 for Sql server.
> Is this true? Is anyone using EMC for Sql log file with Raid 5
> configuration? Is there any whitepaper or artical that specifically talks
> Sql log file on EMC.
> I appreciate your help.
>
>|||How can you say Raid 5 is cheaper than Raid 1 since you need at least 3
drives for Raid 5 and only 2 for a Raid 1. Most controllers do both with
equal ease. I must be missing your point on that one? As for the second
point I basically agree with you in that the larger SANs abstract the actual
disk configurations and have tons of cache to soften the blow so to speak.
But it is still a good idea to to separate the logs from the data and tempdb
when possible. On a busy system it still can bottleneck on the channel or
bus if too much is placed together.
--
Andrew J. Kelly
SQL Server MVP
"Kevin" <ReplyTo@.Newsgroups.only> wrote in message
news:uhUrRpgUDHA.2184@.TK2MSFTNGP10.phx.gbl...
> raid 5 is significantly cheaper than raid 1, even if you only use 3
physical
> disks per array.
> Our experience has been that the very large, very intelligent caching
> engines on enterprise SAN disk devices can make the need for RAID 1 for
> write performance completely moot because nothing gets written through to
> disk synchronously anyway.
> --
> ----
> The views expressed here are my own
> and not of my employer.
> ----
> "Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
> news:O$j$umgUDHA.392@.TK2MSFTNGP11.phx.gbl...
> > Do you mean they want to put the log file and the data on the same Raid
5
> or
> > just 2 different raid 5's. If it's the first then I would make them
prove
> > to you that it can handle the load at your peak transaction rates and
not
> to
> > forget during backups. If you have a low enough transaction rate and a
> fast
> > enough disk subsystem you may not notice but if your going to an EMC
then
> > you most likely have a fair amount of transactions. If they will be on
2
> > different array's and nothing else is on the array with the logs that is
a
> > different story. But Raid 5 is still worse on writes than a Raid 1 and
> > won't save any money since a Raid 1 is usually smaller than a similiar
> Raid
> > 5.
> >
> > --
> >
> > Andrew J. Kelly
> > SQL Server MVP
> >
> >
> > "james" <kush@.brandes.com> wrote in message
> > news:%23nS1c2fUDHA.3308@.tk2msftngp13.phx.gbl...
> > > Hi! Ever since I worked with sql server I have been placing sql log
> files
> > on
> > > Raid 1, which is the recomendation I read everywhere (from books,
> internet
> > > etc).
> > > Now, we are going to use EMC symmetrix DMX and folks here want to save
> > some
> > > money by configuring RAID 5 for both datafile and log file. Their
> > > justification is, EMC DMX is totally different architecture and its
> fast,
> > so
> > > there won't be much difference between Raid5 and Raid1 for Sql server.
> > > Is this true? Is anyone using EMC for Sql log file with Raid 5
> > > configuration? Is there any whitepaper or artical that specifically
> talks
> > > Sql log file on EMC.
> > > I appreciate your help.
> > >
> > >
> > >
> >
> >
>|||Thanks Andrew, Actually its going to be on two different Raid. And they
thought since it will have 16 GB of cache (in EMC), As far as sql server
goes it won't have to concern about Raid configuration underneath. Which
kind of make sense, But still wanted to throw my concern out there and
hoping to find out any White Paper from Microsoft or EMC or any artical
which may explain it in more detail.
thanks again.
"Andrew J. Kelly" <sqlmvpnooospam@.shadhawk.com> wrote in message
news:O$j$umgUDHA.392@.TK2MSFTNGP11.phx.gbl...
> Do you mean they want to put the log file and the data on the same Raid 5
or
> just 2 different raid 5's. If it's the first then I would make them prove
> to you that it can handle the load at your peak transaction rates and not
to
> forget during backups. If you have a low enough transaction rate and a
fast
> enough disk subsystem you may not notice but if your going to an EMC then
> you most likely have a fair amount of transactions. If they will be on 2
> different array's and nothing else is on the array with the logs that is a
> different story. But Raid 5 is still worse on writes than a Raid 1 and
> won't save any money since a Raid 1 is usually smaller than a similiar
Raid
> 5.
> --
> Andrew J. Kelly
> SQL Server MVP
>
> "james" <kush@.brandes.com> wrote in message
> news:%23nS1c2fUDHA.3308@.tk2msftngp13.phx.gbl...
> > Hi! Ever since I worked with sql server I have been placing sql log
files
> on
> > Raid 1, which is the recomendation I read everywhere (from books,
internet
> > etc).
> > Now, we are going to use EMC symmetrix DMX and folks here want to save
> some
> > money by configuring RAID 5 for both datafile and log file. Their
> > justification is, EMC DMX is totally different architecture and its
fast,
> so
> > there won't be much difference between Raid5 and Raid1 for Sql server.
> > Is this true? Is anyone using EMC for Sql log file with Raid 5
> > configuration? Is there any whitepaper or artical that specifically
talks
> > Sql log file on EMC.
> > I appreciate your help.
> >
> >
> >
>