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Any method to check object location: SCM or NVMe?


Yunjae Lee
 

Is there any way to check if an object is allocated in SCM or NVMe?
I installed DAOS in a simple server with Intel DCPMM and NVMe SSD, and I want to compare the I/O performance of the both two cases.


Farrell, Patrick Arthur
 

Yunjae,

The concept of an object being allocated in SCM or NVMe doesn't really apply in DAOS.  If both SCM and NVMe are present, objects will use either one, based on i/o size.

If the i/o size is <4K, the i/o will go to SCM.  If it is greater than or equal to 4K, it will go to NVMe.

It is possible to create a DAOS pool without NVMe (just set the requested size on NVMe to 0).  This allows you to test only SCM.  That would allow some comparisons.  (It is not possible to create a pool without SCM because SCM is required for metadata.)

-Patrick


From: daos@daos.groups.io <daos@daos.groups.io> on behalf of Yunjae Lee <lyj7694@...>
Sent: Monday, September 28, 2020 9:48 AM
To: daos@daos.groups.io <daos@daos.groups.io>
Subject: [daos] Any method to check object location: SCM or NVMe?
 
Is there any way to check if an object is allocated in SCM or NVMe?
I installed DAOS in a simple server with Intel DCPMM and NVMe SSD, and I want to compare the I/O performance of the both two cases.


Yunjae Lee
 

Thanks for the quick reply, Patrick.

I was also wondering how small the I/O size should be to go to SCM rather than NVMe.
I'll test performances following your advice.
It helped me a lot.