IDS Forum

RE: Raw device with Suse Linux Enterpise 10 an....

Posted By: Alexey Sonkin
Date: Thursday, 17 January 2008, at 3:50 p.m.

In Response To: Re: Raw device with Suse Linux Enterpise 10 an.... (Art S. Kagel (Oninit LLC))

Art,

"journaled" file systems should be split into two categories:
1. File systems with full journaling (e.g. JFS (aka VxFS) or
EXT3, when mounted with ' data=journal' flag)
2. File systems with metadata-only journaling (e.g. EXT3
mounted with 'data=ordered')

In the second case, the journaling only slows down the creation
of a file, and doesn't effect the 'normal' Informix operation.
On the other hand, journaling gives you some extra FS protection,
and improves 'fsck' speed after non-clean reboot...
I personally prefer EXT3 with 'data=ordered' to EXT2.

Also, without Direct IO, Cooked (aka block) devices have
bigger overhead, then cooked file system files (might sound strange..)
The reason is that OS cache block size is smaller for block devices,
then for cooked files: on Suse 9, 4k for files and 512 bytes for
block devices. Each OS cache block has an overhead of 96 bytes -
size of block header structure. Clear enough, that, for smaller
blocks, the overhead is more significant
So, without Direct IO, I'd prefer 'cooked file system files'
to 'cooked (block) devices'

To summarize the discussion, I'd suggest the following:
For production system, use RAW devices with Informix, but reference them
through symbolic links. If, in the future, RAW devices become
deprecated,
switch the links to corresponding block devices, and continue with
Direct IO.

For development systems, one can go with EXT3 filesystem, mounted
with 'data=ordered', and Direct IO.

-Alexey

> From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Art S.
> Kagel (Oninit LLC)
>
> Schuran, Sven wrote:
> > Hi,
> >
> > I am setting up a new system.
> >
> > SLES10 with IDS10, what should I prefer raw devices with the raw
module
> > or O_DIRECT support.
> >
> >
>
> Sven,
>
> Personally I still prefer RAW device. It's more secure and even a bit
> or more faster than O_DIRECT. I have softened my position on RAW
> somewhat as the benefits of RAW over O_DIRECT are smaller than over
> normal COOKED devices or filesystems and because of the rumor that
Linus
> had again deprecated RAW devices. But, given that RAW is alive on
Linux
> again, I'll go back to basics. Here's the chunk placement hierarchy
> according to Kagel:
>
> RAW device files are best
> O_DIRECT on COOKED device files is next.
> O_DIRECT on filesystems that support it is third
> COOKED device files is fourth
> COOKED filesystem files on non-journaled filesystems are dead last
> Jounaled filesystems are to be avoided at all costs
>
> Note that while I have extensively tested RAW -vs- COOKED -vs-
> filesystems I have not myself tested O_DIRECT I/O and am relying on
the
> reports of others -- for now.
>
> Art S. Kagel
> Oninit
>
> > Sven
> >
> > <SNIP>
> >
>
>
>
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Messages In This Thread

• Raw device with Suse Linux Enterpise 10 and INform
  Schuran, Sven -- Wednesday, 16 January 2008, at 12:23 p.m.
  • Re: Raw device with Suse Linux Enterpise 10 and IN
    Art S. Kagel (Oninit LLC) -- Wednesday, 16 January 2008, at 12:52 p.m.
    • RE: Raw device with Suse Linux Enterpise 10 an....
      Alexey Sonkin -- Wednesday, 16 January 2008, at 3:38 p.m.
      • Re: Raw device with Suse Linux Enterpise 10 an....
        Art S. Kagel (Oninit LLC) -- Wednesday, 16 January 2008, at 3:56 p.m.
        • RE: Raw device with Suse Linux Enterpise 10 an....
          Schuran, Sven -- Thursday, 17 January 2008, at 2:39 a.m.
          • Re: Raw device with Suse Linux Enterpise 10 an....
            Art S. Kagel (Oninit LLC) -- Thursday, 17 January 2008, at 9:04 a.m.
            • RE: Raw device with Suse Linux Enterpise 10 an....
              Alexey Sonkin -- Thursday, 17 January 2008, at 3:50 p.m.
              • Re: RE: Raw device with Suse Linux Enterpise 10 an
                RICHARD SPITZ -- Tuesday, 5 February 2008, at 6:39 a.m.
                • Re: Raw device with Suse Linux Enterpise 10 an
                  Art S. Kagel (Oninit LLC) -- Tuesday, 5 February 2008, at 6:49 a.m.
                  • RE: Raw device with Suse Linux Enterpise 10 an
                    Robert Roussey(IT) -- Tuesday, 5 February 2008, at 10:21 a.m.
                • RE: RE: Raw device with Suse Linux Enterpise 10 an
                  Noel Murphy -- Tuesday, 5 February 2008, at 7:03 a.m.
                • RE: RE: Raw device with Suse Linux Enterpise 10 an
                  Alexey Sonkin -- Tuesday, 5 February 2008, at 12:08 p.m.
        • RE: Raw device with Suse Linux Enterpise 10 an....
          Schuran, Sven -- Thursday, 17 January 2008, at 2:41 a.m.
        • Re: Raw device with Suse Linux Enterpise 10 an....
          Andreas Breitfeld -- Thursday, 17 January 2008, at 5:24 a.m.
          • Re: Raw device with Suse Linux Enterpise 10 an....
            Art S. Kagel (Oninit LLC) -- Thursday, 17 January 2008, at 9:05 a.m.

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