There's a lot of discussion on the sysctl settings for vfs disk cache/buffers,
but very little consolidated or comprehensive explanations. I have a NAS box with 1GB of memory, but rarely see over ~40MB of utilization during file transfers. When writing a large file to the NAS, I see the transfer rate throttle and pause in regular intervals. This indicates to me the dirty buffers are flushing and writing to the disk, and the file transfer is interrupted during the disk write process. Therefore, I would like to (1) increase the memory utilization, so that a large file write (500MB) will buffer entirely to memory for fastest transfer speeds, and (2) then take as long as needed to write the dirty buffers to the disk, after the transfer is concluded. For part (1), I looked at the following sysctl settings, but I don't fully understand the interactions: vfs.maxbufspace vfs.lobufspace vfs.hibufspace vfs.hidirtybuffers vfs.hirunningspace also /boot/loader.conf kern.nbuf I understand some rules: hirunningspace should be between 1MB to 4MB. lobufspace should be 25% to 75% of hibufspace. What I don't understand is the relationship between maxbufspace and hibufspace, and what are good values. I also don't understand hidirtybuffers. For part (2), I need to slow down the occurrence of sync() or fsync(). Ideally, a sync would not occur for 300 seconds, which is about 10 times as long as (apparently) the default setting. (obviously, if the buffer space is full, a sync would need to occur to make more room.) I've seen references of a daemon to periodically run a sync, or is it controlled by init? Yes, this increases vulnerability when the data is in buffer before committed to disk, but in my application, this is reasonable. _______________________________________________ freebsd-performance@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "[EMAIL PROTECTED]"
