Affects Version/s: Lustre 2.10.4, Lustre 2.10.6, Lustre 2.12.2
Fix Version/s: None
Environment:CentOS 7.6, Lustre/ZFS 2.10.4, 2.10.6, 2.12.2, socklnd and o2ibd
Client partial writes during multi-node N:1 2MB strided writes to striped files. Problem occurs at scale, triggering starts around 50 concurrent files where each file is getting 2MB strided writes from 128 jobs spread across two Lustre client nodes.
Sampling of client side errors:
Lustre + ZFS. 2.10.4, 2.10.6, 2.12.2
2.10.4, 2.10.6, 2.12.2
Socklnd (bonded 40GbE), o2iblnd (FDR & EDR), direct connect and routed o2ib->tcp. 1MB, 4MB and 16MB RPC sizes tested.
References to other JIRA tickets that are or may be related:
A single 600GB file is written to by 128 jobs in a 2MB strided write format. The 128 jobs are spread across two Lustre client nodes.
|Start 1||Start 2||Start 3||Start 4||Start Last|
The file is written with Lustre stripe options of 4-8 OSTs and a stripe_size of 1MB.
With a total number of concurrent files being written being ≤ 30 the partial writes are not experienced. In the case of 30 files being written this would reflect 60 Lustre clients grouped by two with 64 jobs (threads) with each pair writing a different strided file. Using the same scenario but scaled up to concurrent files written ≥ 60 which equates to 120 (or more) Lustre clients in pairs performing strided writes to unique files triggers the partial write scenario.
Making an observation, the combination of the 2MB strided writes and the 1MB OST stripe would result in a significant number of objects per file which scales up as the number of files and concurrent writers increases. Perhaps there is a trigger (I’m spitballing).
Error messages witnessed:
There have been randomly occurring client side error messages. It is not known whether they are resulting in the partial write events or occurring as a result of the partial writes.
No notable server side (MDS / OSS) error messages are observed that would coincide with the partial write errors. The OSS nodes are in an HA configuration and no failovers have occurred as a result of the issue, which if either OSS were becoming overloaded then corosync messages would likely miss and trigger failover.
With 2MB strided writes and 1MB OST stripe size it would seem that certain larger RPC sizes / brw_size / ZFS recordsize combinations could trigger significant write amplification. Perhaps enough to exacerbate the issue.
I have tried to trigger the issue on a testbed filesystem and have ran through permutations of server-side / client-side versions. socklnd and o2ibd direct, o2ibd lnet routed to socklnd, 1 / 4 / 16MB RPC sizes and I cannot trigger the partial write events. Sixteen 64c AMD Rome clients (eight concurrent files written) isn’t enough to trigger it.