[lustre-discuss] Write Performance is Abnormal for max_dirty_mb Value of 2047

Hasan Rashid mrashid2 at uncc.edu
Fri Mar 25 09:45:13 PDT 2022

Hi Everyone,

As the manual suggests, the valid value range for max_dirty_mb is the
values larger than 0 and smaller than the lesser of 2048 MiB or 1/4 of
client RAM. In my system, the client's RAM is 196 GiB.* So, the maximum
valid value for max_dirty_mb(mdm) is 2047 MiB.*

However, when we set the max_dirty_mb value to 2047, *we see very low write
throughput for multiple Filebench workloads that we have tested so far*. I
am providing details for one example of the tested workload below.

*Workload Detail:* We are doing only random write operation of 1MiB size
from one process and one thread to a single large file of 5GiB size.

*Observed Result:* As you can see from the below diagram, as we increase
the mdm value from 768 to 1792 by an amount of 256 in each step, the write
throughput has increased gradually. However, for the mdm value of 2047, the
result dropped very significantly. The observation holds true for all the
workloads we tested so far.

I am unable to figure out why we would have such low performance at the mdm
value of 2047. Please share any insights you have that would be helpful for
me to understand the aforementioned scenario.

Best Wishes,
Md Hasanur Rashid
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lustre.org/pipermail/lustre-discuss-lustre.org/attachments/20220325/c31be010/attachment.html>

More information about the lustre-discuss mailing list