Re: A beginners guide to implementing ASM

I seem to recall that I also ran tests on AWS EC2/EBS Instances.

At this point thought, I do not plan to retest any of this, unless someone makes it part of my official work.

Too many other things to do.

Jared

On Wed, Mar 3, 2021 at 23:32 Andre Maasikas <amaasikas_at_gmail.com> wrote:

> You probably are referring to your blog post and tests a while ago
> where you were using virtualbox with disks presented to guest via ATA
> controller which present them
> with very unusual combination of write cache and no FUA support.
> This was my reply to you directly back then:
>
> As getting posting privs takes time..
> My current assumption is that the difference is because of the interaction
> of
> Oracle device access (O_DIRECT) and specific ATA drive/driver interaction,
> Because of O_DIRECT essentially all write requests have to be flushed
> to disk before
> indication completion to Oracle.
>
> As the ATA drives report write cache (at least in case of vbox and it
> doesn't allow to turn it off)
> and no FUA support, linux kernel has to issue a CACHE FLUSH after
> every write request (or maybe even more)
> - see
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/block/barrier.txt
> and seems it cannot queue more commands inbetween.
>
> So I'v also compiled a custom kernel where I forcibly indicated 'no
> write cache' for ATA drives and
> it brought the performance to the SCSI driver level.
>
> Given that i'm not even sure that the asmfd does 'the right thing'
> given write cache enabled ata drives.
> It might cheat/forget that one has to issue the flushes.
> I dont plan to investigate this further as none of my systems have
> write heavy load or SATA drives :)
> but it was on interesting issue to analyze anyway :)
>
> Andre
>
> On Thu, Mar 4, 2021 at 3:41 AM Jared Still <jkstill_at_gmail.com> wrote:
> >
> >
> > On Fri, Feb 26, 2021 at 7:07 PM Mladen Gogala <gogala.mladen_at_gmail.com>
> wrote:
> >>
> >> I have to say that I prefer the Linux native methods. They are a pain in
> >> the neck (or lower) to set up but I haven't noticed any performance
> >> advantages of the filter driver over the native method, set up by udev
> >> rules.
> >>
> >
> > We will have to agree to disagree on that point. I have measured it,
> and FD is faster than udev rules or ASMLib
> >
> > Jared
> >
> --
> http://www.freelists.org/webpage/oracle-l
>
>
> --

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist Principal Consultant at Pythian
Oracle ACE Alumni
Pythian Blog http://www.pythian.com/blog/author/still/ Github: https://github.com/jkstill

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