RE: FRA f/s block size

From: Amaral, Rui <Rui.Amaral_at_tdsecurities.com>
Date: Mon, 28 Mar 2011 07:15:43 -0400
Message-ID: <1B861F1ABE40A84AA92AD585B20C558B26FA6DAAA1_at_EX7T2-CV06.TDBFG.COM>



For rhel 6 (similar in previous versions as well):

http://people.redhat.com/msnitzer/docs/io-limits.txt

more detail on the block devices files in sysfs:

http://www.mjmwired.net/kernel/Documentation/ABI/testing/sysfs-block

looking at queue size might help performance (depending on your i/o scheduler being used):

http://yoshinorimatsunobu.blogspot.com/2009/04/linux-io-scheduler-queue-size-and.html

one form of linux block tracing:

http://linux.die.net/man/8/blktrace

and example:

http://kb.fusionio.com/KB/a27/howto-capture-a-block-trace-in-linux.aspx

good ole strace also can give io and blocksize requests on running processes.

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Nuno Souto Sent: Monday, March 28, 2011 5:32 AM
To: oracle-l_at_freelists.org
Subject: Re: FRA f/s block size

Thanks Yechiel. That's my gut feel as well.

The only minor snag I can see is that AFAIK the actual I/O size used by RMAN is not documented anywhere. If it is doing 512 units in scatter/gather I/O, then it's virtually the same as 8K blocks - assuming the db is 8k.

Given that it is mostly doing big sequential as you note, it shouldn't matter at all if the last block gets half-filled in case it's doing 8k block I/O.

Ah, I wish I had in Unix the ability to trace actual raw I/O sizes no matter what, like I could in the mainframes...

-- 
Cheers
Nuno Souto
in sunny Sydney, Australia
dbvision_at_iinet.net.au



Yechiel Adar wrote,on my timestamp of 28/03/2011 5:52 PM:

> No experience, just a thought.
> It is used for big sequential writes and no random reads or writes.
> In this case I will used the biggest block I can to minimize the I/Os to the disk.
>
> The reason we use small blocks is to minimize the redundant data transferred to
> memory when you need only one record in the block.
> When you write or read whole blocks, in big sets, use the block size that will
> minimize I/O.
>
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Received on Mon Mar 28 2011 - 06:15:43 CDT

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