[Samba] vfs readahead && windows server 2016/2019?

[Jeremy Allison]

On Mon, Nov 09, 2020 at 07:26:13PM -0500, Robert Buck wrote:
> Hi Jeremy, thank you for your very helpful response. We're looking at a few
> more options. Would you have the time to provide some guidance on these,
> how helpful they may be?

The man pages you're pointing to here are obsolete. All
accurate information is now in the wiki.

>    - *aio ** ->
>    https://www.samba.org/samba/docs/current/man-html/smb.conf.5.html#AIOREADSIZE

Obsolete. All reads/writes should now be done via the pthreadpool. Or
via io_uring.

>    - *write cache* ->
>    https://www.samba.org/samba/docs/current/man-html/smb.conf.5.html#WRITECACHESIZE

Obsolete and code now removed.

>    - *vfs_cacheprime *
>    https://www.samba.org/samba/docs/current/man-html/vfs_cacheprime.8.html

Obsolete. Let the kernel do its thing.

>    - *vfs_full_audit*
>    https://www.samba.org/samba/docs/current/man-html/vfs_full_audit.8.html

All audit code will slow things down :-).

> If you were to rank the likelihood of these helping, how would you rank
> them? Are they still applicable in modern Windows and RHEL?
> 
> Background...
> 
> Our top challenge right now is Windows Explorer, specifically when you get
> properties on a directory, it takes very long to provide a file count, etc,
> comparatively to a share from another Windows Server.
> 
> We just moved all CTDB volatile persistent state to NVMe and we have not
> tested the impact yet, and this may prove significantly beneficial. So the
> Windows Explorer issues may prove to be solved during tomorrow's testing.
> And we're also planning on testing turning off locking in the root folder
> this week, as we've been told this can help a lot too.
> 
> Bear in mind, we are likely to have upwards of 500-800 concurrent users per
> share. We're running in AWS, for both Samba servers and Windows Server
> (desktop streaming).

The meta-data being fetched on directory read is seems like what
is causing problems. Funding Samba to add directory leasing code
will probably help greatly here.