Re: Storage choice for Oracle database on VMware

From: Neil Chandler <neil_chandler_at_hotmail.com>
Date: Wed, 31 Oct 2018 11:29:05 +0000
Message-ID: <AM0PR10MB24509B5A8B88E8529A46887485CD0_at_AM0PR10MB2450.EURPRD10.PROD.OUTLOOK.COM>

Radoulov,

The caching in the SGA understands your data usage patterns through the LRU algorithms and will have cached all of the best data. The FS cache, if you dump it out, will look a lot more like white noise with few discernable patterns. The SAN cache even more so. The more single block reads you have, the more like white noise it all looks. The liklihood of there being a cache hit in the FS or SAN cache is relatively low. The advantage of direct path reads significantly outweights the advantage of both of those caches. It is worth noting in that on most SAN caches, if you specify that the LUN is for a database it will disable read-ahead to pre-populate the cache as it understands that it is not the best use of the cache (the general rule is that SAN cache should be reserved exclusively for writes when the SAN is used for the database.)

Note that these statements are generalisation, and that there may be cases where your assertion is true but they will be an edge case and I would recommend that you have a provable scenario to justify running in that configuration.

Neil Chandler
Database Guy.

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From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on behalf of Radoulov, Dimitre <cichomitiko_at_gmail.com> Sent: 31 October 2018 07:20
To: Andrew Kerber
Cc: lkaing_at_gmail.com; contact_at_soocs.de; Oracle-L Group Subject: Re: Storage choice for Oracle database on VMware

Thank you all for the valuable input!

> what is the problem with direct I/O? You should never run an Oracle database through page cache anyway :)

I'm not sure if direct I/O is always the best choice. I think that certain workloads may benefit from the FS cache.

Anyway, I'm wondering why setall is still not the default value for filesystemio_options on Linux (most probably because of the bugs with certain filesystems and kernel versions).

Regards
Dimitre

Il giorno mar 30 ott 2018, 22:38 Andrew Kerber <andrew.kerber_at_gmail.com<mailto:andrew.kerber_at_gmail.com>> ha scritto: Most places with growing databases and heavy duty environments on vmware use ASM. Some use XFS or similar and LVM, though I am not fond of those.

On Tue, Oct 30, 2018 at 4:34 PM Leng <lkaing_at_gmail.com<mailto:lkaing_at_gmail.com>> wrote: Asm is great when you plan correctly. If you don’t it’s very painful. Eg. If you have different sized disks asm will be forever rebalancing, and failing as there is not enough space on the odd disk. So you need to vacate the diskgroup to rebuild it. (Yes, you know... not my fault, the previous consultant did it...) If there’s an asm bug you may have to take an outage on the Asm to apply the patch.

Normal disk operations like dd to asm is almost impossible. Trying to find that corrupted data block on the asm disk takes great asm expertise from a great oracle support engineer.

Those were some up of my worst asm nightmares. It was only 2 years ago. I have since moved on...

Cheers,
Leng

> On 31 Oct 2018, at 7:20 am, Stefan Koehler <contact_at_soocs.de<mailto:contact_at_soocs.de>> wrote:
>
> Hello Dimitre,
> what is the problem with direct I/O? You should never run an Oracle database through page cache anyway :)
>
> I would go with tweaked XFS (e.g. "nobarrier" as this information is usually not passed through correctly with VMDKs on VMFS, etc.) if it is just one single instance in this VM.
>
> Best Regards
> Stefan Koehler
>
> Independent Oracle performance consultant and researcher
> Website: http://www.soocs.de
> Twitter: _at_OracleSK
>
>> "Radoulov, Dimitre" <cichomitiko_at_gmail.com<mailto:cichomitiko_at_gmail.com>> hat am 30. Oktober 2018 um 19:12 geschrieben:
>>
>> Thank you Chris, Matthew and Niall,
>>
>> so the question is if performancewise ASM is worth it.
>>
>> With the default Oracle database settings the I/O on XFS would be synchronous, right?
>>
>> And if I understand correctly Note 1987437.1, on Linux you cannot enable async I/O without turning on direct I/O too.
>>
>> Regards
>> Dimitre
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Received on Wed Oct 31 2018 - 12:29:05 CET