Community

Subscribe
Highlighted
Accepted Solution

Flash Pool limitations

I have been trying to find some definitive information on flash pool limitations related to ontap 8.1.2/8.1.3 and 8.2

and related to the FAS3250.  However I cannot find anywhere that states what the size limitations are, nor the

number of flash pools that can be on a single controller.

I have heard that there is a 2T per array, 1T per controller, and only one aggregate can have a flash pool.

Can someone point me to a netapp document that spells it out ?

thanks!

---- walter

Re: Flash Pool limitations

Start with this document:

http://www.netapp.com/us/system/pdf-reader.aspx?m=tr-4070.pdf&cc=us

Most questions will be answered.  One that isn't (and I consider important) is what qualifies an I/O as random vs. sequential.  From what I've been told, an I/O that is less than 16K in size is considered random - important because Flash Pools only cache random I/O (as explained in the document I linked to above).  Also, check the Hardware Universe here:

https://hwu.netapp.com/Home/Index

It will show you how much SSD a given HA pair can can accommodate while running CDOT.  For the 3250 per the Hardware Universe it is 4TB.

Hope this helps...

Re: Flash Pool limitations

dcornely1 wrote:

Most questions will be answered.  One that isn't (and I consider important) is what qualifies an I/O as random vs. sequential.  From what I've been told, an I/O that is less than 16K in size is considered random - important because Flash Pools only cache random I/O (as explained in the document I linked to above). 

I see on my install base with, flexscale.lopri_blocks set to off, average read request sizes from Flash Cache that are over 16KB. I therefore think it is less than 32KB.

You can calculate the average request size from e.g. the "stats show -p flexscale-access" output.

Re: Flash Pool limitations

Thanks,

I looked at 4070  and it doesn't answer my questions, tho it should.

I don't see in the hardware universe where it refers to the max ssd.

Which is also affected by the ontap version, not just the hardware itself.

---- walter

Re: Flash Pool limitations

For Hardware Universe start with:

Controllers -> 8.2 (CDOT) -> FAS3250 and then click on "Show Results"

Now you will see a picture of the controller with a bunch of information down below.  About 4 rows down there should be a Flash Pool link.  Click it and it will pop up a window with details about capacity, etc.  Here is a picture for reference.

Re: Flash Pool limitations

Ah!  Perfect, thank you muchly.