From fd56d24725860a3c1f12180cf8503d38d8d0c70d Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Fri, 5 Apr 2024 11:28:55 -0400 Subject: [PATCH] tarfs.5: Provide some guidance on zstd frame sizes Reviewed by: des, emaste MFC after: 2 weeks Sponsored by: Klara, Inc. Differential Revision: https://reviews.freebsd.org/D44636 --- share/man/man5/tarfs.5 | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/share/man/man5/tarfs.5 b/share/man/man5/tarfs.5 index 5378491b9c9f..56c56ac43287 100644 --- a/share/man/man5/tarfs.5 +++ b/share/man/man5/tarfs.5 @@ -74,6 +74,15 @@ to create the tar file, this can be achieved using the and .Cm ztsd:frame-per-file options. +Sensible frame sizes are powers of 2 between the system's base page size +(see +.Xr arch 7 ) +and the value of the +.Sy kern.maxphys +sysctl. +Smaller frames will generally yield a worse compression ratio and require extra +kernel memory to maintain an index, and larger frames will on average require +more CPU time to access data when performing random I/O. .Sh DIAGNOSTICS If enabled by the .Dv TARFS_DEBUG