[osdldbt-general] [Fwd: RE: definition of term "raw device"]

[Mark W. <ma...@os...>]

Doesn't this answer some of the questions we had about SAP DB?

Mark

-----Forwarded Message-----

From: "Mensing, Joerg" <joe...@sa...>
To: 'Martin' <mr...@fr...>
Cc: sap...@li...
Subject: RE: definition of term "raw device"
Date: 04 Nov 2002 09:18:22 +0100

Hi,
since SAPDB does not use any feature of a filesystem for its volumes(alias devspaces) any kind of filesystem overhead including a buffer cache is just an overhead. SAPDB opens using O_SYNC, but O_DIRECT is not yet used. All Read/Write activity use Systempages which are aligned to 4KByte. The LINUX
raw devices which are preferred are those 'unbuffered' /dev/raw/rawX.
CU
jrg

> -----Original Message-----
> From: Martin [mailto:mr...@fr...]
> Sent: Samstag, 2. November 2002 05:54
> To: sap...@li...
> Subject: definition of term "raw device"
> 
> 
> Hi,
> 
> it has occurred to me that the term "raw device" can be 
> interpreted in 
> different ways under linux. There are buffered block devices 
> like /dev/hda, 
> /dev/scd0 etc. and in later kernels unbuffered devices like 
> /dev/raw/raw1 
> etc. that may be bound to the same hardware. Those unbuffered devices 
> require a 512 byte alignment for memory and disk access. 
> 
> My question: can SAPDB use unbuffered devices for dev spaces, 
> and is it 
> advisable to use them? Thanks,
> 
> cu Martin
> _______________________________________________
> sapdb.general mailing list
> sap...@li...
> http://listserv.sap.com/mailman/listinfo/sapdb.general
> 
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