performance of block device - raw device

[Thiyagarajan.s]

hi
i want to know which will have good performance Raw / block device and where can i find this documents

raw device are used for swap and oracle but how this imporves the performance

Thanks
Thiyagarajan

[Peter Godron]

Hi,
if you are having a performance problem with oracle and raw devices make sure your kernel parameter max_async_ports is set as high as possible.
Oracle will use async to write to raw until the limit is reached, then switch to sync writes.

I prefer block devices as I am more used to working with them and I can control everthing from sam ( I know I'm lazy....)

[Thiyagarajan.s]

Peter
Thanks for your response
i want to know the generic information of raw and block device

mean while i will go through the doc for kernal parameters

Thanks
Thiyagarajan

[Peter Godron · Accepted solution]

Hi,
have not found a proper document on this, but a simple explanation:

"Raw" devices are Character devices.
"Cooked" devices are block devices.

The difference is that "Cooked" devices are accessed thru the OS with
standard "read" and "write" commands. Since they are accessed through the
operating system, the OS will handle the underlying raw device's structure
and allow you to create files and directories on the raw device. Because
they are easier to use, there is a (slight) performance tradeoff.

"Raw" devices can be read from and written to as well, but they are single
"files". You cannot create files and directories within a raw device
(unless you write complex software to do so, and if you were to do that you
might as well use a cooked device).

The only time that there is a noticeable difference is with large databases.
Sybase, Oracle, Ingres, etc allow the use of Raw devices because they can
squeeze out a 10-15% performance kick on heavily read/write intensive
operations. The tradeoff is that Raw devices are much harder to manage from
the OS, because from the OS's perspective they are simply "unused" disk.

Put another way, raw/cooked is the oldest tradeoff in the computing world:

Speed vs. Ease of use
Quote from Kent Smith

Hope this answers your question ;-)

[Rita C Workman]

I've heard that one touted by vendors more than I care to think.
But I think Clay said it well at this thread, and maybe you'll appreciate it too:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=62288

Rgrds,
Rita

[Thiyagarajan.s]

hi peter / Rita

Thanks for your reply
i will be more equipped if i have a document can anyone help me for finding docs of concepts of HP - ux related