From eab82c5772d4f764a84620eae738784ba24f5f64 Mon Sep 17 00:00:00 2001 From: Matthew Dillon Date: Fri, 11 Sep 2009 12:18:42 -0700 Subject: [PATCH] HAMMER - Update hammer.5 manual page * Add a description of how the bioq sysctls can be adjusted to give reads an even higher priority over writes. --- share/man/man5/hammer.5 | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/share/man/man5/hammer.5 b/share/man/man5/hammer.5 index d6e93bf9fa..99abc9b63a 100644 --- a/share/man/man5/hammer.5 +++ b/share/man/man5/hammer.5 @@ -436,6 +436,35 @@ Add to .%O http://www.dragonflybsd.org/hammer/nycbsdcon/ .%T "Slideshow from NYCBSDCon 2008" .Re +.Sh FILESYSTEM PERFORMANCE +The +.Nm +file system has a front-end which processes VNOPS and issues necessary +block reads from disk, and a back-end which handles meta-data updates +on-media and performs all meta-data write operations. Bulk file write +operations are handled by the front-end. +Because +.Nm +defers meta-data updates virtually no meta-data read operations will be +issued by the frontend while writing large amounts of data to the filesystem +or even when creating new files or directories, and even though the +kernel prioritizes reads over writes the fact that writes are cached by +the drive itself tends to lead to excessive priority given to writes. +.Pp +There are four bioq sysctls which can be adjusted to give reads a higher +priority: +.Bd -literal -offset indent +kern.bioq_reorder_minor_bytes: 262144 +kern.bioq_reorder_burst_bytes: 3000000 +kern.bioq_reorder_minor_interval: 5 +kern.bioq_reorder_burst_interval: 60 +.Ed +.Pp +If a higher read priority is desired it is recommended that the +.Fa kern.bioq_reorder_minor_interval +be increased to 15, 30, or even 60, and the +.Fa kern.bioq_reorder_burst_bytes +be decreased to 262144 or 524288. .Sh HISTORY The .Nm -- 2.11.4.GIT