macOS SMB Speed Throttling & Network Share File Pollution

Resolving 10x SMB throughput drops caused by mandatory packet signing (/etc/nsmb.conf) and preventing .DS_Store / AppleDouble pollution.

Trap 1: The SMB Packet Signing Speed Throttle

Starting with macOS 10.13.4 High Sierra, Apple configured the macOS SMB client to force packet signing (signing_req=yes) on every outbound SMB connection by default.

The Symptom:

When connecting a Mac to a TrueNAS, Synology, Windows Server, or Samba share over 1GbE, 2.5GbE, or 10GbE LAN:

• Transfer speeds plummet from 110 MB/s down to 15-25 MB/s.
• CPU usage spikes on both the Mac and the NAS as cryptographic hashes are generated for every single data frame.

The Remediation:

Disable mandatory SMB packet signing in /etc/nsmb.conf:

sudo tee /etc/nsmb.conf << 'EOF'
[default]
signing_req=no
EOF

*Disconnect the network share and reconnect. LAN transfer speeds will immediately return to line-rate (110+ MB/s on 1GbE, 280+ MB/s on 2.5GbE, 1+ GB/s on 10GbE).*

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Trap 2: .DS_Store and ._* AppleDouble Pollution

Every time macOS Finder navigates into a folder on a network share, it creates:

1. .DS_Store: Stores desktop view preferences, icon sizes, and scroll positions.

2. ._<filename>: AppleDouble sidecar files created on filesystems that lack native macOS extended attributes.

The Problem:

Windows and Linux users see folders littered with hundreds of hidden dotfiles, triggering sync conflicts and cluttered backups.

The Remediation:

Instruct macOS Finder never to create .DS_Store files on network shares:

defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool TRUE

Restart Finder for the setting to take effect:

killall Finder