HDD slow performance when syncthing is running

Hi Everybody, first post

I’ve just started using syncthing and it’s been great, but my issue is HDD (mechanical) slows a lot, from 40mb’s/s to 1mb’s

I’ve tried disabling “watch for changes” in advanced settings in the share folder

Anyone knows if there is a way to improve performance?


Is that as soon as Syncthing runs or only when the configured folder(s) is(/are) being synchronised? I don’t think that there should be a lot of continues Syncthing-related HDD-activity when the watcher is disabled. Does the task-manager/top show what process makes excessive use of the hard drive?

I’m not sure about specific configuration items to tweak for relatively slow hard drives, as I don’t have any device using those anymore. But there is a configuration-tuning page in the docs which you can read through, to check what makes sense for your use-case;


But perhaps someone with experience of running Syncthing on relatively slow systems has better and more specific input.

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I forgot to mention, syncthing is running on an arm powered orange-pi 5 with 8Gb of ram and 2 HDD, 2.5" 5TB and 10TB 3.5"

The biggest question: is your Syncthing database also on one of the HDDs?

Thanks for replying! The orange pi 5 has an 256gb nvme ssd (300mb/s)

The HDD’s are connected via USB

Are you sure the slowdown is only due to the HDDs and not other factors? The CPU used in your device seems rather weak (see https://www.cpubenchmark.net/cpu.php?cpu=Rockchip+RK3588), and Syncthing is very CPU heavy as well.

USB can be a contributing bottleneck depending on the adapter being used (I’m assuming that both HDDs are SATA.

Some additional details that would help a lot:

  • Make/model of both 2.5" and 3.5" HDDs.
  • Make/model of the USB enclosures if the two HDDs were purchases as bare drives.
  • Are both HDDs affected by the slow performance?
  • Number of files being managed by Syncthing.

Based on what’s known so far, given the drive capacities, one or both of the HDDs might be using SMR (shingled magnetic recording) and not CMR (conventional magnetic recording).

Hi, thanks for the answer.

Both HDD are WD hdd with the proprietary enclosures, the 5TB is SMR and is USB, the other has a WD enclosure but internally I imagine it’s a sata drive, the bigger drive performance is a lot higher, I guess being 3.5" and CMR.

I’m currently using only one, the 5TB one

WD sometimes modifies their drives, attaching the USB-to-SATA bridge directly to the drive (without a SATA connector) instead to save on costs.

Ah, SMR drives often have similar read performance to comparable CMR drives, but random non-sequential writes is where it becomes I/O bound.

SMR drives are fine for archival storage such as backups, but applications such as Syncthing, Dropbox, rclone, rsync and so on that are updating existing files don’t work as well.

How is the 2.5" 5TB drive formatted? (e.g. NTFS, ext4,…)

SMR disks via USB paired with a low powered host is roughly the worst case scenario.

Probably my best option would be to move to another 10TB CMR drive that seems to perform a lot better

If upgrading to a CMR drive is an option, it’d be the best long-term solution. Otherwise, a few tips when using a SMR drive:

  • In Linux, set the noatime mount option to reduce the number of random writes (most distros either use the default atime or take a middle approach with relatime).
  • Use a filesystem with COW (Copy-on-Write) support, or at least one that tries to reduce file fragmentation.
  • Newer Linux kernels and filesystems such as btrfs (since version 5.12) support optimizations for zoned storage used by SMR and some NVMe drives.

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