Fine tuning 2026.10.26

CiCADA tuning, round 2

Based on the server info collected at 19:33 KST and the analyzer run at 19:38 on 26 Oct 2026.

Verdict

The server is idle and healthy: load 0.02, no CPU, memory or I/O pressure, PHP-FPM peaked at 3 of 7 workers per pool, OPcache hit rate 99.93%, InnoDB miss rate 0.16%, no slow queries and no nginx errors. More throughput tuning would not be measurable. What is left is one real latency item (cloud's data sits on a USB hard disk), a few configuration mistakes worth fixing, and housekeeping.

1. Heavy Nextcloud jobs run in the daytime

maintenance_window_start is 1, which means 01:00 to 05:00 UTC, or 10:00 to 14:00 KST. Move it to 02:00 to 06:00 KST (UTC 17):

for d in cloud.onni.me air.meson.in; do
  sudo -u www-data php8.4 /var/www/$d/occ config:system:set maintenance_window_start --type=integer --value=17
done

The Monday backups (03:00 to 03:30) overlap with it once a week. Use 19 instead for 04:00 to 08:00 KST if you prefer.

2. Two cron lines probably fail every 5 minutes

previewgenerator is disabled on both instances, but the www-data crontab still calls occ preview:pre-generate every 5 minutes. Test it:

sudo -u www-data php8.4 /var/www/cloud.onni.me/occ preview:pre-generate

If it says the command is not defined, either run occ app:enable previewgenerator on that instance, or delete the two lines with sudo crontab -u www-data -e. Each failing run boots the whole Nextcloud framework for nothing, and the output goes to /dev/null so you never see it.

3. cloud.onni.me data lives on the slow disk

iostat (average since boot) shows sdc, the USB hard disk mounted at /home/web-data, at 38 ms read and 31 ms write latency, against 0.5 to 0.9 ms for your SSDs. The cloud instance keeps its data and temp directory there, while its database is on the SSD. Few reads were sampled, so treat the figure as indicative, but it is the only place a user could feel slowness.

a) Monitor the disk. SMART output for sdc was blank, so that disk is not being checked. USB bridges need SAT mode:

sudo smartctl -d sat -H -A /dev/sdc

b) Stop atime writes. In /etc/fstab, add noatime to the options of the /home/web-data line (keep your UUID and the other fields, for example defaults,noatime,commit=60), then:

sudo mount -o remount,noatime /home/web-data
findmnt /home/web-data

c) Larger read-ahead for the rotational disks (128 KB today) helps large file downloads:

sudo tee /etc/udev/rules.d/60-hdd-readahead.rules >/dev/null <<'EOF'
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/read_ahead_kb}="1024"
EOF
sudo udevadm control --reload && sudo udevadm trigger --subsystem-match=block --action=change
cat /sys/block/sdc/queue/read_ahead_kb

d) Keep cloud's temp files off that disk (air already uses the SSD):

sudo install -d -o www-data -g www-data -m 750 /home/www-data/.tempdir-cloud
sudo -u www-data php8.4 /var/www/cloud.onni.me/occ config:system:set tempdirectory --value=/home/www-data/.tempdir-cloud

e) Measure before deciding anything bigger. If the previews are small, they could later move to the SSD:

sudo du -sh /home/web-data/cloud.onni.me/appdata_*/preview

4. Kernel settings

sudo tee /etc/sysctl.d/99-local.conf >/dev/null <<'EOF'
vm.swappiness = 10
vm.vfs_cache_pressure = 50
vm.overcommit_memory = 1
net.ipv4.tcp_congestion_control = bbr
net.ipv4.tcp_slow_start_after_idle = 0
net.core.rmem_max = 2500000
net.core.wmem_max = 2500000
EOF
echo tcp_bbr | sudo tee /etc/modules-load.d/bbr.conf
sudo modprobe tcp_bbr && sudo sysctl --system
sysctl net.ipv4.tcp_congestion_control vm.swappiness

Why each line:

5. MariaDB: remove one line

log_bin is off, so binlog_format = ROW does nothing and logs a warning at every start ('You need to use --log-bin to make --binlog-format work'):

sudo sed -i 's/^binlog_format/#binlog_format/' /etc/mysql/mariadb.conf.d/50-server.cnf

It takes effect at the next restart, so there is no need to restart just for this. Optional: reclaim the 45 MB of free space in cloud's activity table with OPTIMIZE TABLE oc_activity; in the cloud database.

Everything else matches what the numbers need: the buffer pool is 65% free with a 99.8% hit rate, and at most 4 of 60 connections were ever used.

6. PHP: two tiny trims

Do these only when you restart PHP-FPM for another reason:

Then run sudo systemctl restart php8.4-fpm. Keep the pool sizes (peak 3 of 7) and OPcache at 192 MB (72% used).

7. Redis eviction policy

Change maxmemory-policy allkeys-lru to volatile-lru in /etc/redis/redis.conf. Nextcloud locks and cache entries carry expiry times, so they stay evictable, and nothing without an expiry can be dropped by accident. Redis holds 1.9 MB of 256 MB, so this is protection, not tuning:

sudo sed -i 's/^maxmemory-policy .*/maxmemory-policy volatile-lru/' /etc/redis/redis.conf
sudo systemctl restart redis-server

Restart at a quiet moment, because file locks are dropped.

8. Docker

The torrent containers have no resource limits and unbounded logs. In /home/www-data/bit.onni.me/docker-compose.yaml, add this to each transmission service:

    mem_limit: 512m
    cpus: 1.5
    cpu_shares: 256
    logging:
      driver: json-file
      options:
        max-size: 10m
        max-file: "3"

Add only the logging: block to the gluetun service. Then apply:

cd /home/www-data/bit.onni.me && docker compose up -d

Compose recreates only the services that changed. Per-service logging avoids restarting dockerd, and a daemon restart would stop every container because live restore is off. cpu_shares: 256 (default 1024) lets Nextcloud win under CPU contention. Optional: docker image prune frees 1.36 GB of unused images.

9. Journal size

The journal is 1.3 GB and journald holds 105 MB of RAM:

sudo mkdir -p /etc/systemd/journald.conf.d
sudo tee /etc/systemd/journald.conf.d/size.conf >/dev/null <<'EOF'
[Journal]
SystemMaxUse=200M
MaxRetentionSec=1month
EOF
sudo systemctl restart systemd-journald
sudo journalctl --vacuum-size=200M

10. Services you may not need

11. Watch list (no change now)

cd /var/www/cloud.onni.me
LOG="$(sudo -u www-data php8.4 occ config:system:get datadirectory)/nextcloud.log"
sudo jq -r 'select(.level>=3)|[.app,.message]|@tsv' "$LOG" | cut -c1-150 | sort | uniq -c | sort -rn | head
sudo jq -r 'select(.level<2)|.app' "$LOG" | sort | uniq -c | sort -rn | head

Leave as is

PHP-FPM pool sizes and memory limits, OPcache at 192M, the InnoDB buffer pool (512M), the temp-table and full-join figures (they come from schema checks), nginx (HTTP/3, buffers, gzip, headers, zero errors), the CPU governor (schedutil) and the I/O schedulers.

Revision #1
Created 2026-10-26 13:04:47 UTC by meson
Updated 2026-10-26 13:05:25 UTC by meson