Adding FastCache on Online Machine,will there be Perf issues ?

Question

Hi , I don't know if to created the FAST Cache in the middle of the day or not at one of the customer, could it impact while adding it to the Cache ? (currently no FAST enabled)

lblanclozano · Answer

I/O profiles to use Fast Cache (take only as a reference): SQL - Yes except LOGS DataBase LOGs - No SharePoint - Selective VDI - Yes NFS / CIFS - Selective Exchange - with NL-SAS Sequential - No

RRR · Answer

And you are aware that not all I/O profiles are suitable for FAST Cache? It's great for random I/o and bad for sequential, but I guess you know that, right?

Jim_Hegner · Answer

Hi.

There can be two different answers to your question.

If the system does not have FAST CACHE setup:

Adding FAST CACHE to an existing VNX will take up some of the Memory of each SP. So during the Warm up of the Fast Cache there may be a small performance impact due to a lower amount of available SP memory.

This will be more visible on the First Gen VNX than on the Next Gen VNX due to the differences in the way FAST CACHE fills up...

I would set this up at the end of the Work day, or during a period of low activity on the System..

If the system already have FAST CACHE Enabled and you want to expand the available disk Space to use for FAST CACHE.

To do this you need to destroy the CACHE already set up, and rebuild FAST CACHE with the new number of SSD.

This will more often than not have a impact on the system, due to the fact that all data in the FAST CACHE needs to be flushed, and that can take some time depending on the setup of the array...(Hours)

RRR · Answer

Also consider that it will take a so called 'warm-up time' for FAST Cache to fill up with data. On the new VNX this will be quicker than the first VNX generation, but still it's good to know that you won't benefit from the extra performance right away. Depending on the activity on the system this can take several hours. During this time you shouldn't notice any impact on performance other than it will gradually get better.

Jyothi_P_Bharat · Answer

Hi,

You can also refer to the document:

https://support.emc.com/docu35244_White-Paper:-EMC-Performance-for-Oracle-—-EMC-VNX,-Enterprise-Flash-Drives,-FAST-Cache,-VMware-vSphere.pdf?language=en_US

Thanks

Jyothi

alkhvo · Answer

Hi

Hope you have installed Fast Cache enabler. If not youshould install it, but each SP will reboot one at a time.

If enabler is already installed, there no any perfomance issue when you enable Fast Cache. But if I were you i would turn it on during peak-off hours.

Alex

Tsky · Answer

Thanks alot for the help, Avout the profiles y know , just wanted to know if it has some kind of impact in the warm-up phase or not ,altough i will wait to off-peak time.

dynamox · Answer

if i remember correctly you may need to go back and enable FAST Cache for Flare LUNs/Pools that were in the array prior to FC installation.

Jim_Hegner · Answer

Dynamox you are correct, one will need to manually enable FAST CACHE for every Storage pool or Raid Group LUN on the system after it is enabled.

If this is a system with lots of RG LUNs this can be scripted as it could take some time to do LUN by LUN...

Going forward after the installation the standard is that all pools or LUNs start with FC enabled

RRR · Answer

... where FC stands for FAST Cache. Yes, you might want to check that to be sure.

VNX

Adding FastCache on Online Machine,will there be Perf issues ?

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