IDS Forum

Re: define raw device on Redhat Linux

Posted By: FRANK
Date: Wednesday, 13 October 2010, at 10:25 p.m.

In Response To: Re: define raw device on Redhat Linux (Art Kagel)

Thanks a lot, Art!

Sorry not gave the description clearly.

This is a brand new installation and testing.

(1) created a new db root chunk ( the only one we created) pointed to the
raw character device defined by the system administrator. It was the only
chunk we defined for the instance that was used for every thing : root
dbs, logical/physical log, data .......
(2) created a new table in the chunk, started a looping script that
just kept inserting new row into the table
(3) pulled out the two disk driver cables( physically cut the disk
connection, so NO DISK available now!) that bridged Disk to EMC
Powerpath. The RedHat connected to EMC powerpath. IDS was not impacted,
stayed online as normal.
(4) we saw the loop script job paused for around 20 seconds...., then
resumed doing the inserting job perfectly......
(5)IDS keep working continuously without any sense of disk failure during
the whole procedure. ( Logical log completed one by one.....)

So, we think the IDS was cheated somehow... and data was taken by a
Middleman..... So, we are looking for the Middleman...

Thanks,
Frank

On Wed, Oct 13, 2010 at 7:45 PM, Art Kagel <art.kagel@gmail.com> wrote:

> Frank,
>
> The problem is not your RAW device definitions, it is your understanding of
> what Informix is doing and how it does transactions. Remember that Informix
> ONLY works on data pages that are in its cache, so as long as the data that
> is being modified by your transactions is already in cache (or would be on
> a
> new page and so only written initially to cache) Informix will not be
> modifying the chunks on disk and will not realize that the disk has gone
> bad. Dirty pages are flushed to disk when the lru_min/max_dirty thresholds
> are reached or during or after a checkpoint. There is one exception.
> Logical and physical log pages are immediately written to disk. You could
> try destroying the raw partition or physically removing the disk drive for
> the logical logs and see what happens, but that's not going to get you
> quicker responses for the other chunks.
>
> Also, is it possible that the engine is actually still able to write to the
> device after you disabled the device drivers? Perhaps the OS is maintaining
> the path to the raw device even with the device driver removed because a
> process has the device open. Your test may not be valid. Try physically
> removing or powering down the drive itself.
>
> Art
>
> Art S. Kagel
> Advanced DataTools (www.advancedatatools.com)
> IIUG Board of Directors (art@iiug.org)
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and
> do not reflect on my employer, Advanced DataTools, the IIUG, nor any other
> organization with which I am associated either explicitly, implicitly, or
> by
> inference. Neither do those opinions reflect those of other individuals
> affiliated with any entity with which I am affiliated nor those of the
> entities themselves.
>
> On Wed, Oct 13, 2010 at 6:44 PM, FRANK <yunyaoqu@gmail.com> wrote:
>
> > Thanks, Andreas.
> > I give more detailed on this problem.
> >
> > We are setting up the IDS11.50 FC7 of RedHat Linux 5, using EMC Clariion
> > disk.
> > The Sysadmin defined the raw disk (character device), and Logical
> Volumes.
> >
> > We did the test to make sure the data would not be buffered(should be
> > written to disk immediately) when the transaction is committed.
> >
> > But, the result is that, after we disabled the disk drivers, IDS keeps
> > running and committing transactions.... So , the committed data is
> > buffered somewhere....
> >
> > We want to know what is the problem, wrong character device defined? Red
> > Hat and EMC?, or other?......
> >
> > Basically, How to setup Redhat/EMC raw character device to make sure it
> > does not buffer data when there is a disk problem , so IDS can abort the
> > job immediately.
> >
> > Thanks
> > Frank
> >
> > On Wed, Oct 13, 2010 at 5:08 AM, Andreas Breitfeld <abreitfe@de.ibm.com
> > >wrote:
> >
> > > On Tuesday 12 October 2010 19:30:59 FRANK wrote:
> > > > Folks,
> > > >
> > > > IDS11.50 FC7, Redhat Linux5
> > > >
> > > > Our sysadmin is working on Logical volume definition for our new EMC
> > > > Clarion ... Disk.
> > > > We saw http://www.informix-zone.com/node/38 is a good paper for
> > getting
> > > > a Character device ( not Block device) in Suse Linux.
> > > > Just, want to check if there is more such type of info ... on Redhat
> > ...
> > > If O_DIRECT is an option for you:
> > >
> > >
> >
> http://dbaspot.com/forums/informix/147617-how-setup-block-devices-o_direct-
> > > rhel5.html
> > >
> > > Thanks,
> > > Andreas
> > >
> > > >
> > > > Thanks,
> > > > Frank
> > > >
> > > > --001485f274e2cfbabd04926ed644
> > > >
> > > >
> > > >
> > >
> >
> ***************************************************************************
> > > > **** Forum Note: Use "Reply" to post a response in the discussion
> > forum.
> > > >
> > >
> > > --
> > > Andreas Breitfeld; Informix Development Munich
> > > IBM Deutschland Research & Development GmbH; Vorsitzender des
> > > Aufsichtsrats:
> > > Martin Jetter; Geschaeftsfuehrung: Dirk Wittkopp; Sitz der
> Gesellschaft:
> > > Boeblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294
> > >
> > >
> > >
> > >
> >
> >
>
> *******************************************************************************
> > > Forum Note: Use "Reply" to post a response in the discussion forum.
> > >
> > >
> >
> > --001485f1e44090f7b8049287541a
> >
> >
> >
> >
>
> *******************************************************************************
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
> >
>
> --0016361e81deaa5bc10492883076
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--001485f03cac6f58c504928a6acd

Messages In This Thread

• define raw device on Redhat Linux
  FRANK -- Tuesday, 12 October 2010, at 1:30 p.m.
  • Re: define raw device on Redhat Linux
    rroussey@comcast.net -- Tuesday, 12 October 2010, at 1:52 p.m.
    • Re: define raw device on Redhat Linux
      FRANK -- Wednesday, 13 October 2010, at 6:45 p.m.
  • Re: define raw device on Redhat Linux
    Andreas Breitfeld -- Wednesday, 13 October 2010, at 5:08 a.m.
    • Re: define raw device on Redhat Linux
      FRANK -- Wednesday, 13 October 2010, at 6:44 p.m.
      • Re: define raw device on Redhat Linux
        Art Kagel -- Wednesday, 13 October 2010, at 7:45 p.m.
        • Re: define raw device on Redhat Linux
          FRANK -- Wednesday, 13 October 2010, at 10:25 p.m.
          • Re: define raw device on Redhat Linux
            FRANK -- Friday, 15 October 2010, at 11:01 a.m.

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