TRIM and changing mount options

Dan Nelson dnelson at
Wed Jul 24 03:00:10 UTC 2013

In the last episode (Jul 23), aurfalien said:
> I've some what blindly followed a how to on installing FreeBSD 9.1 on a
> ZFS mirror.
> My typing is horrid so I simply ssh'd to a live CD env and pasted line by
> line as per the how to found here;
> All is well, no issues with replacing disks, testing failures etc...
> But seeing that my system drives are SSDs, I thought to perhaps add
> noatime, etc...  to avoid slow downs common in excessive SSD usage.
> However my fstab is only mounting swap partitions and I have no idea how
> my file system is being mounted :)
> Also, I would like to use tunefs in finding if I have TRIM enabled as I
> did load it via boot.conf
> I kinda feel like I'm willy nilly adding load lines w/o seeing if I
> actually have the TRIM patch installed :)
> At any rate, could some one;
> a) Explain how I am loading my file system as I'm used to fstab?
> b) How to run tunefs on my zroot
> c) How to determine if I actually have the needed TRIM support in my kernel

ZFS automatically opens pools that were previously imported ( this info is
stored in /boot/zfs/zpool.cache ), and automatically mounts any filesystems
that have a mountpoint specified, so fstab isn't needed.

Tunefs is a UFS-only command, so it won't help you here.  Most zfs
properties can be set on the fly with the "zfs" command.  You can disable
atime on your ZFS filesytem with "zfs set atime=off zroot".  All the
filesystems created in zpool will inherit the value.

I'm not sure if there's a way to query TRIM status on arbitrary geom
providers, but you can see whether zfs successfully sent any TRIM requests
by watching the output of "sysctl kstat.zfs.misc.zio_trim".  If
.zio_trim.success increments and .unsupported (or .failed) doesn't, then you
know that it's working.

	Dan Nelson
	dnelson at

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