[lustre-discuss] how to mapping of RPC rate to bandwidth/IOPS?

Andreas Dilger adilger at whamcloud.com
Tue Jun 9 20:00:14 PDT 2020

On Jun 2, 2020, at 02:30, 肖正刚 <guru.novice at gmail.com<mailto:guru.novice at gmail.com>> wrote:

Hi all,
we use TBF policy(details: https://jira.whamcloud.com/secure/attachment/14201/Lustre%20NRS%20TBF%20documentation%200.1.pdf) to limit rpcrate coming from clients; but I do not know how to mapping of rpcrate to bandwidth or iops.
For example:
if I set a client's rpcrate=10,how much bandwith or iops the client can get  in theory?

Currently, the TBF policies only deal with RPCs.  For most systems today, you are probably using 4MB RPC size (osc.*.max_pages_per_rpc=1024), so if you set rpcrate=10 the clients will be able to get at most 40MB/s (assuming applications do relatively linear IO).  If applications have small random IOPS then rpcrate=10 may get up to 256 4KB writes per RPC, or about 2560 IOPS = 10MB/s.

Cheers, Andreas
Andreas Dilger
Principal Lustre Architect

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