ONTAP Hardware

Difference between adding individual SSD disks to aggr or creating a storage pool for cache?


This is my first time setting up a cDOT system, FAS8040 with 8.3, and also SSD cache. Have a couple of questions.


Here's our setup.

Node A has the aggregate of SAS disks

Node B has the aggregate of SATA disks


We have a single DS2246 of 200GB SSD drives we want to use for caching and also creat a small aggregate for moving volumes in for patching and maintenance.


First, setting up the SSD flash pool --> As I understand it you can add the individual SSD disks right to the aggregate in its own RAID group typically RAID4. Or you can instead create a storage pool of SSDs and use that as the cache disks for an aggregate. Which way would be better? What are the pros and cons of either adding the disks individually or in a storage pool.


Second, how do you create an aggregate with SSD disks in System Manager 8.3? When I go to create an aggregate it does not show the SSD disks to choose from.


And a final question about SSD cache. I remember reading that you can select which volumes you want to participate with SSD caching. How do you do that?


Storage pool allows sharing of SSD capacity between multiple aggregates (even on different controllers); If you have just one aggregate, traditional flash pool is easier to manage.

I am not aware of a possibility to disable caching for individual volumes.


Thank you for explaining this to me.


Follow up, also want to create a small aggregate of SSD but when I go to create an aggregate in System Manager I do not see the SSD drives. Just the SAS and SATA disks. Do I have to create this through CLI?

Are SSD disks assigned to this controller?


You can remove Volumes from caching by using this command:


# volume modify -vserver VSERVER -volume VOLUME -caching-policy none


or adding again by 


# volume modify -vserver VSERVER -volume VOLUME -caching-policy auto


I never used System Manager to do something so I can't help you there.


I would recommend to use the whole SSDs and not Storage Pools if possible and not sharing SSDs between different aggrs.


# volume modify -vserver VSERVER -volume VOLUME -caching-policy none

You are right of course. It allows also more fine-grained control than just all or nothing. Thank you for correcting!