Just another thought here. If the debug output files fit in an inode, then these would be handled as metadata updates to the inode, which is typically much smaller than the file system blocksize. Looking at my storage that handles GPFS metadata shows avg KiB/IO at a horrendous 5-12 KiB!
HTH, -B -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Peter Serocka Sent: Wednesday, April 11, 2018 6:07 AM To: gpfsug main discussion list <[email protected]> Subject: Re: [gpfsug-discuss] Confusing I/O Behavior Note: External Email ------------------------------------------------- Let’s keep in mind that line buffering is a concept within the standard C library; if every log line triggers one write(2) system call, and it’s not direct io, then multiple write still get coalesced into few larger disk writes (as with the dd example). A logging application might choose to close(2) a log file after each write(2) — that produces a different scenario, where the file system might guarantee that the data has been written to disk when close(2) return a success. (Local Linux file systems do not do this with default mounts, but networked filesystems usually do.) Aaron, can you trace your application to see what is going on in terms of system calls? — Peter > On 2018 Apr 10 Tue, at 18:28, Marc A Kaplan <[email protected]> wrote: > > Debug messages are typically unbuffered or "line buffered". If that is > truly causing a performance problem AND you still want to collect the > messages -- you'll need to find a better way to channel and collect those > messages. > > > _______________________________________________ > gpfsug-discuss mailing list > gpfsug-discuss at spectrumscale.org > http://gpfsug.org/mailman/listinfo/gpfsug-discuss _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss ________________________________ Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you are hereby notified that any review, dissemination or copying of this email is strictly prohibited, and to please notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. The Company, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request or solicitation of any kind to buy, sell, subscribe, redeem or perform any type of transaction of a financial product. _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
