FreeBSD 11.1 Beta 2 ZFS performance degradation on SSDs

[Caza, Aaron]

I've been  having a problem with FreeBSD ZFS SSD performance inexplicably degrading after < 24  hours uptime as described in a separate e-mail thread.  In an effort to get down to basics, I've now performed a ZFS-on-Root install of FreeBSD 11.1 Beta 2 amd64 using the default Auto(ZFS) install using the default 4k sector emulation (vfs.zfs.min_auto_ashift=12) setting (no swap, not encrypted).

Firstly, the vfs.zfs.min_auto_ashift=12 is set correctly in the /boot/loader.conf file, but doesn't appear to work because when I log in and do "systctl -a | grep min_auto_ashift" it's set to 9 and not 12 as expected.  I tried setting it to vfs.zfs.min_auto_ashift="12" in /boot/loader.conf but that didn't make any difference so I finally just added it to /etc/sysctl.conf where it seems to work.  So, something needs to be changed to make this functionaly work correctly.

Next, after reboot I was expecting somewhere in the neighborhood of 950MB/s from the ZFS mirrored zpool of 2 Samsung 850 Pro 256GB SSDs that I'm using as I was previously seeing this before with my previous FreeBSD 11-Stable setup which, admittedly, is a different from the way the bsdinstall script does it.  However, I'm seeing half that on bootup.

Performance result:
Starting 'dd' test of large file...please wait
16000+0 records in
16000+0 records out
16777216000 bytes transferred in 37.407043 secs (448504207 bytes/sec)

Zpool Status:
  pool: zroot
state: ONLINE
  scan: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        zroot       ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            ada0p2  ONLINE       0     0     0
            ada1p2  ONLINE       0     0     0

/boot/loader.conf:
kern.geom.label.disk_ident.enable="0"
kern.geom.label.gptid.enable="0"
vfs.zfs.min_auto_ashift=12
vfs.zfs.arc_min="50M"
vfs.zfs.arc_max="51M"
zfs_load="YES"

/etc/sysctl.conf:
vfs.zfs.min_auto_ashift=12


Is this the expected behavior now in FreeBSD 11.1?

--
Aaron
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