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set dsync and directio options according to device type

Posted on 2016-10-19
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Last Modified: 2016-10-20
Dears, what does mean the 'unknown device type' in description column in the result of sp_helpdevice ?

And for these devices, is it preferred to set dsync option to true and directio to false.

Are those two options (dsync and directio) affect on transaction log devices which are file system devices??
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Question by:suzn cas
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4 Comments
 
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Expert Comment

by:Joe Woodhouse
ID: 41851407
Can you show me a sample line of sp_helpdevice output?

Generally it is better to have directio true and dsync false if you have an OS and file system type that supports directio.

If you are using any kind of file system devices, we want at least one of those options to be true (exception - devices used for tempdb where we want both to be false). directio is better performance than dsync.

If you use raw partitions the options are ignored, effectively all raw partition i/o is directio anyway.
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Author Comment

by:suzn cas
ID: 41851498
Dear Joe,

kindly note the attached file, on the same location I stored log device (in its description: file system device), and data device (in its description: unknown device type).

Thank you.
sp_helpdevice-result.png
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Joe Woodhouse earned 500 total points
ID: 41851738
Huh! That's very interesting. Normally that happens only for things like tape drives.

I had a look in the documentation for sp_helpdevice as well as the documentation for master..sysdevices where that descrption field is populated from. For disk it should not show that.

I'm not sure it actually matters, maybe for some reason sp_helpdevice has gotten confused. I'm sorry, I don't think I have an answer for you on this one. :(

Probably the only way to find this out is to open a support case with SAP.
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Author Closing Comment

by:suzn cas
ID: 41851763
Dear Joe,
No problem, Thank you very much
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