Eddy

I  have been contributing to an,  as yet, unpublished  whitepaper testing FASTCache. Best if I include a couple of quotes from it

1. "Oracle archive files and redo log files have a predictable workload composed mainly of sequential writes. These can be efficiently handled by the array’s write cache and assigned HDDs. Enabling FAST Cache on these files is neither beneficial nor cost effective."

Similarly there is little or no benefit assigning Flash to your redo when it is handled by an array’s write cache .

2. "In line with EMC recommendations, FAST Cache was enabled for the Oracle data files only."

Also you can look at the following whitepaper on Powerlink

Oracle database on EMC VNX Best Practices

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h8242-deploying-oracle-vnx-wp.pdf

hope this helps answer your question

Allanr, thanks for you helpful information.

I have a bit further question on this thread.

As my understanding on Redo, every modification on data files would generate at least 2 updates on Redo , although DB write process would append redo file in seq write, every single SSD provide closely 300MB/s through put, about 6-7x faster than SAS spindle.

Any comments?

Thanks,

Eddy

As per my previous reply,

"Similarly there is little or no benefit assigning Flash to your redo when it is handled by an array’s write cache"

Allan

I do not disagree with this part. I just think it is a bit idealized. VNX SP cache is running within “high water mark” and “low water mark”, if amount of Redo file update is not huge, SP cache is good, otherwise, it would drive it into “forced flush”, that could affect host performance.

EFD performance is more sustained, considering cost, SAS spindles w/ SP write cache is relatively good choice.

Thoughts?

Eddy

Eddy

here is a great post by EMC's Kevin Closson which discusses redo logging in depth  and should address your question regarding redo and flash

http://kevinclosson.wordpress.com/2007/07/21/manly-men-only-use-solid-state-disk-for-redo-logging-lgwr-io-is-simple-but-not-lgwr-processing/

today I looked @ ODA configuration, it is with 292GB Flash for redo log. comments?

Yes

ODA has no array cache

https://community.emc.com/message/563946#563946

This url is for Exadata but I hope you will pick up the general idea

http://jarneil.wordpress.com/2012/03/20/exadata-smart-flash-logging/

Ok, got it, that makes sense.

I was wrong, I thought ODA storage SN was a server, but no, it is a shared SAS JOB.

I find a document describe its HW components well, see the link, www.artimbilisim.com/bulten/ODA-VAD-VAR-Tech.pps

Eddy