[gpfsug-discuss] Maxblocksize tuning alternatives/max number of buffers

[Valleru, Lohit/Information Systems]

Hello Everyone,

I am looking for alternative tuning parameters that could do the same job as tuning the maxblocksize parameter.

One of our users run a deep learning application on GPUs, that does the following IO pattern:

It needs to read random small sections about 4K in size from about 20,000 to 100,000 files of each 100M to 200M size.

When performance tuning for the above application on a 16M filesystem and comparing it to various other file system block sizes - I realized that the performance degradation that I see might be related to the number of buffers.

I observed that the performance varies widely depending on what maxblocksize parameter I use.
For example, using a 16M maxblocksize for a 512K or a 1M block size filesystem differs widely from using a 512K or 1M maxblocksize for a  512K or a 1M block size filesystem.

The reason I believe might be related to the number of buffers that I could keep on the client side, but I am not sure if that is the all that the maxblocksize is affecting.

We have different file system block sizes in our environment ranging from 512K, 1M and 16M.

We also use storage clusters and compute clusters design.

Now in order to mount the 16M filesystem along with the other filesystems on compute clusters - we had to keep the maxblocksize to be 16M - no matter what the file system block size.

I see that I get maximum performance for this application from a 512K block size filesystem and a 512K maxblocksize.
However, I will not be able to mount this filesystem along with the other filesystems because I will need to change the maxblocksize to 16M in order to mount the other filesystems of 16M block size.

I am thinking if there is anything else that can do the same job as maxblocksize parameter.

I was thinking about the parameters like maxBufferDescs for a 16M maxblocksize, but I believe it would need a lot more pagepool to keep the same number of buffers as would be needed for a 512k maxblocksize.

May I know if there is any other parameter that could help me the same as maxblocksize, and the side effects of the same?

Thank you,
Lohit