Re: Latest recommendation for asmlib + number of LUNs
- From: Niall Litchfield <niall.litchfield@xxxxxxxxx>
- To: Chris Stephens <Chris.Stephens@xxxxxxx>
- Date: Thu, 15 Aug 2013 11:14:33 +0100
As you say you'll encounter at least 2 different opinions. I fall into the
"don't think its worth it" camp, so bear that in mind in what follows. We
also use it exclusively here for our RAC systems - haven't got that
standard rewritten as yet :)
Technically in 11.x asmlib only provides 2 features, both of which I would
argue are available without it.
1) it provides an exclusive I/O interface to the device
2) it labels the disk so that there is persistent naming for the device.
That's it. It's worth remembering that ASMLIB was born in 2004 when async
i/o and persistent device naming on Linux platforms was, errm, deficient.
Those conditions just aren't true today. Disk labelling and aliasing is
built into both multipath and udev on Linux and works perfectly well to
ensure that Oracle always finds the same devices at the same name. In
addition ASMLIB consists both of a userland and kernel module, consequently
if you patch the O/S kernel - say for security reasons - then you *will*
have to update asmlib each and every time as well. In many cases the *you*
that has to do this will be your sys admin team, in the case of base O/S
packages this shouldn't be an issue. In addition as of RHEL/OEL 6 asmlib is
pre-compiled only for the Unbreakable Enterprise Kernel supplied by Oracle,
you should probably be using this to be honest, but many people won't be.
For these reasons I see asmlib as an extra layer requiring maintenance and
providing no added value.
Definitely read https://blogs.oracle.com/wim/entry/asmlib for a definitive
background. Now Oracle could, and indeed to some extent (on Oracle
hardware) has enhanced asmlib to provide further features - see
http://www.scaleabilities.co.uk/2013/02/07/diagnosing-asmlib/ for an
example.
On Wed, Aug 14, 2013 at 8:34 PM, Stephens, Chris <Chris.Stephens@xxxxxxx>wrote:
> I'm venturing into the land of Oracle RAC for the first time and will be
> installing an 11.2.0.3 2-Node cluster from scratch. The storage will be
> allocated from a Dell Compellent (not sure if that's relevant to my
> question or not).
> The official documentation recommends the use of ASMLib but I seem to
> remember a lot of folks on here thinking that was a bad idea or at least
> not a no brainer.
>
> What's the current recommendation / bestest idea on ASMLib use?
>
> Also, any recommendation on the number of LUN's to start off with for each
> disk group? (+data, +fra) Oracle recommends a minimum of 4 but I'm not
> sure how they arrived at that number or whether more would be advantageous.
> That's probably an "it depends" question so what info do I need to make
> that determination?
>
> Thanks,
> Chris
>
>
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--
Niall Litchfield
Oracle DBA
http://www.orawin.info
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