filesystem dbfile vs raw device dbfile

filesystem dbfile vs raw device dbfile

Post by a950961 » Mon, 19 Feb 2001 13:10:22



Hi,

I have a stupid questions...

are raw device dbfile in unix means character device or it means block
device?

also, what will be the benefits using raw device dbfile? speed?
relaiablity?

thx all experts.

^_^

 
 
 

filesystem dbfile vs raw device dbfile

Post by Lee Kyoung Ro » Mon, 19 Feb 2001 23:03:00


raw device is character device.
And the benefits using raw device defile is performance that did not use
file system cache mechanism.
But Solaris and HP-UX support file system mount without filesystem cache.
Good luck to U!


Quote:> Hi,

> I have a stupid questions...

> are raw device dbfile in unix means character device or it means block
> device?

> also, what will be the benefits using raw device dbfile? speed?
> relaiablity?

> thx all experts.

> ^_^


 
 
 

filesystem dbfile vs raw device dbfile

Post by Spence » Tue, 20 Feb 2001 07:57:34


on HP-UX, "raw" means a character device, which is really
a "logical volume" in a "volume group". e.g.  /dev/vg01/rlvol3

on HP-UX, by using "raw" instead of file system files, Oracle
can use asynchronous i/o (via the ascync driver), and avoid
the overhead/bottlenecks associated with a file system.  any
improvement in performance will likely be unnoticeable on a
lightly loaded system, and less than 10% under a heavy load.

while some tout the inability to use standard os commands to
manipulate raw partitions as a "disadvantage", i actually find
this to be an "advantage" of raw partitions.  for example, the
"rm" command cannot be used to remove a raw partition from
the system.


Quote:> Hi,

> I have a stupid questions...

> are raw device dbfile in unix means character device or it means block
> device?

> also, what will be the benefits using raw device dbfile? speed?
> relaiablity?

> thx all experts.

> ^_^

 
 
 

filesystem dbfile vs raw device dbfile

Post by Nuno Sou » Tue, 20 Feb 2001 17:10:05




Quote:>on HP-UX, by using "raw" instead of file system files, Oracle
>can use asynchronous i/o (via the ascync driver), and avoid
>the overhead/bottlenecks associated with a file system.  any
>improvement in performance will likely be unnoticeable on a
>lightly loaded system, and less than 10% under a heavy load.

Depends.  *If* you installed all the patches that make all that work,
*if* you setup everything the right way, *if* your filesystem cache
hit pattern matches what your database applications are doing, *then*
you *may* get less than 10% diff under heavy load.  

IME, you get in any given UNIX system around 30% less CPU usage
(that's right, CPU) when going raw, assuming that you were on standard
"vanilla" file systems to start with.  Of course, if you are patient
enough to chase up all the patches needed (both ORACLE and UNIX), then
it may pay off to go async I/O and ignore raw.  But it takes a while
to get everything pointed the right way...

Problem is that too many measure the wrong things when comparing raw
to file system.  (not saying you do, just making a general comment).

Quote:

>while some tout the inability to use standard os commands to
>manipulate raw partitions as a "disadvantage", i actually find
>this to be an "advantage" of raw partitions.  for example, the
>"rm" command cannot be used to remove a raw partition from
>the system.

Good point.

Cheers
Nuno Souto

http://www.users.bigpond.net.au/the_Den/index.html