Problems with 3Gb switch
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4 way box, sql 2kent sp3a, w2kadv server sp3 + hotixes, active/passive cluster, local disks + san for data, oltp database(s) approx 500 users + com etc.
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We had some issues with a cluster after enabling the 3GB switch and using more memory. Prior using 2 Gb ram, sql approx 1.7Gb - after, using 3 Gb ram , sql approx 2.7 Gb. memory on the box never went above 3 Gb used. No AWE enabled.
Anybody had problems after adding more memory to the server ( databases about 27 Gb )
[font="Comic Sans MS"]The GrumpyOldDBA[/font]
www.grumpyolddba.co.uk
http://sqlblogcasts.com/blogs/grumpyolddba/ -
From BOL:
"Standard 32-bit addresses can map a maximum of 4 GB of memory. The standard address spaces of 32-bit Microsoft Windows NT® 4.0 and Windows 2000 processes are therefore limited to 4-GB. By default, 2 GB is reserved for the operating system, and 2 GB is made available to the application. If you specify a /3GB switch in the Boot.ini file of Windows NT Enterprise Edition or Windows 2000 Advanced Server, the operating system reserves only 1 GB of the address space, and the application can access up to 3 GB. For more information about the /3GB switch, see Windows NT Enterprise Edition or Windows 2000 Advanced Server Help."
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If you only have 3Gb RAM don't use the /3GB switch, only use this is you have 4Gb RAM.
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Server(s) have 4Gb ram, config checked by microsoft system engineer - I'm interested if anyone has had problems after increasing the available ram to a SQL Server using an oltp database.
[font="Comic Sans MS"]The GrumpyOldDBA[/font]
www.grumpyolddba.co.uk
http://sqlblogcasts.com/blogs/grumpyolddba/ -
A related question - We have a 4 Gb server with the 3Gb switch not enabled and SQL Server memory dynamically configured with a max of 2GB. SQL Server memory stays at 1.7Gb. If the OS uses 2Gb do you know what uses the remaining 300 MB?
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What you most likely have is 2gb ram sat on the server resting its electrons
Check the memory usage for the box in task manager, it probably won't be much above 2Gb.
Enabling the 3gb switch will allow sql server to use up to 3Gb ram, in practice it tends to use 2.7Gb - you can monitor the remaining memoryeasily in task manager.
Extra memory should speed up the server as more pages get cached, you may see cpu usage rise however, but overall things should go faster.
[font="Comic Sans MS"]The GrumpyOldDBA[/font]
www.grumpyolddba.co.uk
http://sqlblogcasts.com/blogs/grumpyolddba/ -
The only problem we had was that our SCSI tape driver could not handle the /3GB switch, which meant that our backups failed until we could find the problem and replace the driver.
Here is the code we used to enable AWE for SQL Server:
sp_configure ' show advanced options', 1
reconfigure
go
sp_configure 'awe enabled', 1
reconfigure
go
sp_configure 'max server memory', 7168
reconfigure
go
(Restart SQL Server)
Compaq Support told use to be aware that once awe is enabled, Task Manager no longer accurately reports the amount of memory used by SQL Server; you can determine the amount of memory used by SQL Server with the following query:
select cntr_value, cntr_type from sysperfinfo
where
object_name = 'SQLServer:Memory Manager' and
counter_name = 'Total Server Memory (KB)'
You might want to watch the following "SQLServer:Buffer Manager" counters in Performance Monitor:
- AWE lookup maps/sec
- AWE stolen maps/sec
- AWE unmap calls/sec
- AWE unmap pages/sec
- AWE write maps/sec
- Buffer cache hit ratio
Jon
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The tape drive problem is interesting - I wonder if the san storage drivers had a problem - the microsoft engineers reported a problems with poor disk response - I'll check it out, thanks.
[font="Comic Sans MS"]The GrumpyOldDBA[/font]
www.grumpyolddba.co.uk
http://sqlblogcasts.com/blogs/grumpyolddba/
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