non-buffered I/O in Linux?

Alex Daniloff

4 Jun 2002 4 Jun '02

07:19

Hello SuSE folkz, Does somebody know if Linux kernel allows to perform non-buffered I/O on raw disk partitions? In documentation on InnoDB tables it said: By using a raw disk you can on some Unixes perform unbuffered I/O. I assume that it should improve DB performance. Thank you in advance for any thoughts or sources of information. Alex -- MS Windows users should be covered under the Americans with Disabilities Act! --------------> Try Linux and you'll understand why <--------------

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Christopher Mahmood

4 Jun 4 Jun

08:46

New subject: [SLE] non-buffered I/O in Linux?

* Alex Daniloff (alex@daniloff.com) [020603 23:19]:

...

Does somebody know if Linux kernel allows to perform non-buffered I/O on raw disk partitions?

I'm not sure what the status is in the vanilla kernel but the SuSE kernel has had it for some time. I think the LVM whitepaper on www.suse.com has something on setting it up. -- -ckm

Jerry Feldman

15:01

New subject: [SLE] non-buffered I/O in Linux?

There is some history there. On Unix systems, block devices are implemented with entries as both a block as well as a character (raw) device. You will see in /dev devices like: crw------- 1 root system 8, 2 Feb 2 2001 /dev/rrz0c brw------- 1 root system 8, 2 Feb 2 2001 /dev/rz0c The raw device is not necessarily unbuffered, but the device driver handles it in a much different manner than as a block device. However, Linus himself did not like the raw device concept. As far as specialized I/O operations are concerned, databases can use varous tools, such as ioctl(2) and fctl(2) to control I/O. On 3 Jun 2002 at 22:19, Alex Daniloff wrote:

...

Does somebody know if Linux kernel allows to perform non-buffered I/O on raw disk partitions? In documentation on InnoDB tables it said: By using a raw disk you can on some Unixes perform unbuffered I/O. I assume that it should improve DB performance. Thank you in advance for any thoughts or sources of information.

-- Jerry Feldman Enterprise Systems Group Hewlett-Packard Company 200 Forest Street MRO1-3/F1 Marlboro, Ma. 01752 508-467-4315 http://www.testdrive.compaq.com/linux/

Graham Smith

16:22

New subject: [SLE] non-buffered I/O in Linux?

On Tuesday 04 June 2002 15:19, Alex Daniloff wrote:

...

Hello SuSE folkz, Does somebody know if Linux kernel allows to perform non-buffered I/O on raw disk partitions? In documentation on InnoDB tables it said: By using a raw disk you can on some Unixes perform unbuffered I/O. I assume that it should improve DB performance. Thank you in advance for any thoughts or sources of information. Alex Hi Alex,

There was an extensive thread on this subject on the linux-informix mailing list a while back. The following is an email sent by Reinhard Habichtsberg on how to setup raw devices on Linux. I have not tried to configure raw devices, but hope this information helps. Also I suggest you do a search on google for "raw devices linux". ---------------------------------------------------------------------------------------- To: "'Linux-Informix-Liste'" Date: Fri, 22 Mar 2002 19:15:24 +0100 Hi, today we configured a new database server and took the chance to use raw devices. Distribution: SuSE 7.3 Kernel: 2.4.10-64SMP For SuSE one has to: - edit /etc/rc.config and set ACTIVATE_RAW_DEV="yes" - edit /etc/raw: example: # /etc/raw # # sample configuration to bind raw devices # to block devices # # The format of this file is: # raw<N>:<blockdev> # # example: # --------- # raw1:hdb1 # # this means: bind /dev/raw/raw1 to /dev/hdb1 # # ... raw2:rd/c0d2p1 raw3:rd/c0d2p2 raw4:rd/c0d2p3 ... To activate the bindings: /etc/init.d/raw start or reboot. Change owner and group of /dev/raw/raw? to informix and perms to 660. We have a RAID 10 disk array, the cooked devices reside in /dev/rd and their seems to be no problems. Alternatively one can use the raw command to create the bindings, for example: raw /dev/raw/raw2 /dev/rd/c0d2p1 raw /dev/raw/raw3 /dev/rd/c0d2p2 raw /dev/raw/raw4 /dev/rd/c0d2p3 ... Put this commands in a shell script and call it during boot procedure because the bindings will be lost when the server is halted. raw -qa shows the current configuration. Reinhard --------------------------------------------------------------------------------- Regards, Graham Smith ---------------------------------------------------------

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Alex Daniloff
Christopher Mahmood
Graham Smith
Jerry Feldman