Re: SSDs and LUNs

What you would normally do is to increase the number of paths to the storage, and use the mpath device as your ASM disk. You'll get an O/S queue per path that way. It is, of course, possible to generate queueing within the array by being over enthusiastic.

As a point of reference, we are happy with larger LUNS (4tb) and more paths for our all flash array based databases. If you do use LUN sizes larger than 2T *and* use ACFS make sure you are on a current version ( > 12.1.0.2.5) otherwise once your ACFS filesystem gets more than 2T of data added to it, you'll lose it all :(
https://support.oracle.com/epmos/faces/DocumentDisplay?id=2065748.1

On Thu, Oct 19, 2017 at 8:09 PM, Ram Raman <veeeraman_at_gmail.com> wrote:

>
> "If there is a layer at which you have a single queue to each LUN you will
> have an I/O bottleneck" is exactly what I am thinking of. just 2 queues for
> TB of data?
>
> Let me read up on the link Connor emailed.
>
> Rich J: I cannot understand your question since those terms sound new to
> me. I will have to research that.
>
> Mladen: It is going to be in house, not on cloud. and 1.5Tb LUNs are
> common (with SSDs?)? How is the IO in those installations? I understand
> that SSDs outperform HDDs, but I am wondering, just wondering, that by
> providing 2 or 4 luns we are losing the advantage that SSDs give us?
>
>
> On Thu, Oct 19, 2017 at 1:39 AM, Jonathan Lewis <
> jonathan_at_jlcomp.demon.co.uk> wrote:
>
>>
>> At some layer between Oracle and the silicon the various software
>> components will have some queues. If there is a layer at which you have a
>> single queue to each LUN you will have an I/O bottleneck when you've got
>> lots of Oracle processes trying to read from just 2 (or 4) LUNs.
>>
>> I'm not an expert with stuff that far away from the Oracle software but I
>> would be a little surprised if you got bad performance because you were
>> configured as 40 LUNs, while I have seen bad performance from a system
>> where the solid state SAN had been configured as just 2 LUNs (one for data,
>> one for redo).
>>
>>
>> Regards
>> Jonathan Lewis
>>
>> ________________________________________
>> From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on
>> behalf of Ram Raman <veeeraman_at_gmail.com>
>> Sent: 19 October 2017 06:49:23
>> To: ORACLE-L
>> Subject: SSDs and LUNs
>>
>> We are moving one of the systems to vm. The consultants who have been
>> hired to do the implementation are recommending that we create just 2 or 4
>> 'LUNS' for data diskgroup for the db that is 3Tb in size which exhibits
>> hybrid IO. They are promising it is best rather than having 30 or 40 LUNs
>> since the new disks will all be SSDs.They are claiming that it will perform
>> better than having 40 'LUNs'. I still have the 'old way of thinking' when
>> it comes to IO. Can someone confirm one way or other, or point to any
>> paper. thanks.
>>
>> Ram.
>>
>> --
>>
>>
>>
>
>
> --
>
>
>

-- 
Niall Litchfield
Oracle DBA
http://www.orawin.info

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