Hi John, are you asking about the Hybrid IO feature in 2.16+ Lustre releases, or something else?
There is a client-side "llite.*.hybrid_io" parameter that can enable/disable Hybrid IO on a client completely, and the llite.*.hybrid_io_write_threshold_bytes and llite.*.hybrid_io_read_threshold_bytes can be used to tune the IO size threshold where IO changes between buffered and direct. Applications can of course use open(O_DIRECT) to use DIO instead of buffered IO. As for the server-side non-buffered IO path, this is controlled by the osd-ldiskfs.*.readcache_max_io_mb and .writethrough_max_io_mb parameters, both default to 8 MiB. Note that flash (non-rotational) OSTs disable read and write cache entirely by default, since NVMe devices are typically fast enough to handle incoming IO. I don't think there is any way for clients to fetch these parameters directly, since they are more a property of the OST than the client. Cheers, Andreas On Jan 9, 2026, at 14:32, John Bauer <[email protected] <mailto:[email protected]>> wrote: > > Hello all, > Is the a way to determine what size a client I/O request must be to trigger > the OSS to use the Large File ( non-buffered ) I/O path? Is this > configurable? > Is there a way for a client-side application to trigger this behavior > independent of the I/O size? --- Andreas Dilger Principal Lustre Architect [email protected] _______________________________________________ lustre-discuss mailing list [email protected] http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
