multiple files for 1 group but same "disk"... performance?

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Jéjé - 16 Aug 2005 00:44 GMT

Hi,

To try to improve my performance on a system where I have no control (a long
long story...)

My problem:
the HD subsystem is "bad", I'm on a SAN and most of my wait types are caused
by the disks.
I have only 1 disk available (300gb in Raid 5, but I don't know how many
disks behind this)

so I have 1 partition for my database!!! (the throughput is bad)
My server has 4 processors (8 with HT enabled)

I know that SQL perform better if I have 1 file by processor because SQL
server create 1 thread by file (I'm right?)
so, if I create 8 files but all in the same group, does this help me?

if yes, how can I redistribute the usage of my current tables, which are in
only 1 file for the moment, on all files (without having to copy the tables
in a new table)

or I have to create 8 groups with 1 file only and choose which table I put
in which group?

or this idea will improove... nothing!

thanks.

jerome

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Myles.Matheson@gmail.com - 16 Aug 2005 12:41 GMT

Hello Jeje,

Seems we are in the same boat, I too have a large SAN with RAID 5 and
500 gb over 10 disks.

The optimization I have gone with is creating file groups for large
tables and sperate file groups for indexes.

Eg
FactSalesData -fact table data
FactSalesIndex - fact table index

You can only specify a file group for a table to use; you can't
specify the file as far as I know.

One other thing to consider is the use of logical drives on you single
partition, this will allow you to stream the disk queues via the OS,
well that's the theory.

So with sperate file groups for indexes and data you should reduce the
file lock contention.

For more tips on file groups see
http://www.sql-server-performance.com/filegroups.asp

Also check out http://www.sql-server-performance.com/ew_san.asp

It has some great ideas on SAN configuration.

Hope this helps,

Myles Matheson
Data Warehouse Architect
http://bi-on-sql-server.blogspot.com/

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Jéjé - 16 Aug 2005 13:11 GMT

thanks

do you see any improvement?

my firsts tests wher I divide my primary group into 8 files don't change
anything (or a too small change)

I'll try to use separated filegroups.

> Hello Jeje,
>
[quoted text clipped - 30 lines]
> Data Warehouse Architect
> http://bi-on-sql-server.blogspot.com/

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