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@xxxxxxxxx> wrote:
You probably are referring to your blog post and tests a while agoJared Still
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@xxxxxxxxx> wrote:
wrote:
On Fri, Feb 26, 2021 at 7:07 PM Mladen Gogala <gogala.mladen@xxxxxxxxx>
and FD is faster than udev rules or ASMLib
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,
--
Jared
//www.freelists.org/webpage/oracle-l
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