FreeBSD 11.1 Beta 2 ZFS performance degradation on SSDs

[Steven Hartland]

vfs.zfs.min_auto_ashift is a sysctl only its not a tuneable, so setting it in /boot/loader.conf won't have any effect.

There's no need for it to be a tuneable as it only effects vdevs when they are created, which an only be done once the system is running.

You don't explain why you believe there is degrading performance?

What is the exact dd command your running as that can have a huge impact on performance.


On 19/06/2017 23:14, Caza, Aaron wrote:
> 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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