Date: Tue, 16 Mar 2010 01:40:25 +0200 From: Dan Naumov <dan.naumov@gmail.com> To: freebsd-questions@freebsd.org, freebsd-fs@freebsd.org Subject: Some questions about vfs.zfs.prefetch_disable=1 and ZFS filesystem versions Message-ID: <cf9b1ee01003151640u57b99e23rd0045ba57b82f94d@mail.gmail.com>
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After looking at the arc_summary.pl script (found at http://jhell.googlecode.com/files/arc_summary.pl), I have realized that my system has set vfs.zfs.prefetch_disable=1 by default, looking at dmesg, I see: ========================= ZFS NOTICE: Prefetch is disabled by default if less than 4GB of RAM is present; to enable, add "vfs.zfs.prefetch_disable=0" to /boot/loader.conf. ========================= ...except I do have 4gb of RAM. Is this caused by integrated GPU snatching some of my memory at boot? From dmesg: ========================= real memory = 4294967296 (4096 MB) avail memory = 4088082432 (3898 MB) ========================= What kind of things does this tunable affect and how much of a performance impact does enabling / disabling it have? Should I manually enable it? I've also noticed a really weird inconsistency, my dmesg says the following: ========================= ZFS filesystem version 13 ZFS storage pool version 13 ========================= Yet: ========================= zfs get version NAME PROPERTY VALUE SOURCE cerberus version 3 - cerberus/DATA version 3 - cerberus/ROOT version 3 - cerberus/ROOT/cerberus version 3 - cerberus/home version 3 - cerberus/home/atombsd version 3 - cerberus/home/friction version 3 - cerberus/home/jago version 3 - cerberus/home/karni version 3 - cerberus/tmp version 3 - cerberus/usr-local version 3 - cerberus/usr-obj version 3 - cerberus/usr-ports version 3 - cerberus/usr-ports-distfiles version 3 - cerberus/usr-src version 3 - cerberus/var version 3 - cerberus/var-db version 3 - cerberus/var-log version 3 - cerberus/var-tmp version 3 - ========================= Is this normal or should "zfs get version" also show version 13? This is on a system with the pool and filesystems created with 8.0-RELEASE, by the way. Thanks! - Sincerely, Dan Naumov
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