Extremely Slow Sync Speed (drops to 15KB/sec)

[robotech]

dear Forum members:
I’m experiencing extremely slow sync speeds while running a mirror job ( around 20000 small files to an external SSD). Initially, transfer speed is decent for a few seconds, but over time, it drops drastically—even as low as 15KB/sec.
I have tried adjusting the thread count (tested with 1, 2, and 4 threads), but performance remains poor.

FreeFileSync Version: 14.0 (same case with previous releases)
OS: Windows
external SSD: USB-C, top notch SSD.

Is there any setting in FreeFileSync that could help maintain higher sync speeds? Could this be due to the large number of small files, or is there another possible bottleneck? Any advice would be greatly appreciated.
thanks.

Screenshot 2025-02-10 174951.jpg (136.21 KiB) Viewed 959 times

[xCSxXenon]

Doesn't seem out of the ordinary to me. The write cache could be full, or it could just be from a lot of small files. Check Task Manager, should tell you where the bottleneck is. Look for "Active Time" for the drives. The one at 100% is the bottleneck

[robotech]

Doesn't seem out of the ordinary to me. The write cache could be full, or it could just be from a lot of small files. Check Task Manager, should tell you where the bottleneck is. Look for "Active Time" for the drives. The one at 100% is the bottleneck

none of drives are 100%. they are around 2%.

[robotech]

is this normal behavior of this tool? it takes hours to mirror only a couple of GB data. is robocopy faster comparing with freefilesync?

[xCSxXenon]

FFS has never been the bottleneck in the many years I've been on this forum. Unlikely this will be the first

[robotech]

FFS has never been the bottleneck in the many years I've been on this forum. Unlikely this will be the first

when I'm mirroring large size files, it maintains good speed. it slows down while transferring small size files. i could not find any issue in task manager or disk performance.
what other factor can play a role in this?
thanks

[xCSxXenon]

The USB-SATA controller, the SSD controller itself, the NAND architecture, the USB protocol stack overhead on your system, failing storage. Have you actually tried changing any of the hardware involved for testing? What is this "USB-C, top notch SSD" you speak of? Top notch isn't a spec

[robotech]

The USB-SATA controller, the SSD controller itself, the NAND architecture, the USB protocol stack overhead on your system, failing storage. Have you actually tried changing any of the hardware involved for testing? What is this "USB-C, top notch SSD" you speak of? Top notch isn't a spec

top notch meant that it is not a usb1.0 interface disk or decade old hardware. this is sandisk extreme pro connected with usb-c, tested with connecting to thunderbolt port, i tested with a thumb drive, with a samsung T7 SSD, tried using a different cable to connect to SSD.
I did a couple of more test with hooking up a nvme inside a enclosure and that has way better result. so it is indicating may be something is up with USB controller or bridge inside the SSD, running out cache or something.

[xCSxXenon]

https://shop.sandisk.com/products/ssd/portable-ssd/portable-ssd-sandisk-extreme-pro-usb-3-2?sku=SDSSDE81-1T00-G25
Looks like there was a pretty bad firmware issue if they explicitly address it and new models are differentiated from old ones! See if you can update it

[robotech]

fix:
reformatted drive from exFAT to NTFS and it works way faster, I'm talking ~x20 times in my case where number of files is in thousands.
apparently some of the performance functions like Trim and garbage collection does not work with exFAT.
however there will be some limitation on NTFS for OS supports, but i don't care for this one. new Linux based OS these days support NTFS anyway.

[therube]

Maybe it had to do with something like cluster size?
Most likely (?) exFAT was using 128 KB, where NTFS is using 4 KB.
And then compounding the issue is the small sizes of the files you were syncing.

There seems to be reasons for exFAT's large cluster size, Why is exFAT's default allocation size in Windows so high?

[konicsek]

I run FFS 14.0 donation on a Win 11 Pro with an internal Samsung 990 Pro and external Samsung T9 with special cable and USB C 3.2
FFS ist extremly fast. It takes seconds to compare a million files, and seconds to copy 10 thousands of files.
that is incredible !!

with dual boot on the same machine, ubuntu 24.04.2 LTS, the same job takes about 5 Minutes to compare only 500.000 files, the top window showing the progress of files shows the files on the usbdrive (internal drive is fast)
playing with threads makes no difference, afterwards copy is quite fast,
I have to adjust the directories for the usb drive: instead of [T9] on Windows I use /media/xxx/T9 on ubuntu
filesystem is exfat
read with lsusb
Bus 002 Device 002: ID 04e8:61fd Samsung Electronics Co., Ltd PSSD T9
Bus 002.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/5p, 20000M/x2
|__ Port 001: Dev 002, If 0, Class=Mass Storage, Driver=uas, 20000M/x2

I don't know what to do

[Georg]

Hallo zusammen,
ich habe den externen Speicher auf NTFS umgestellt. Fazit das Programm ist mit Version 14.2 nicht mehr zu gebrauchen. Es ist weiterhin beim Spiegeln extrem langsam. 25GB in 3 Tage ist haltlos.

[konicsek]

problem solved:
exFAT is extremly slow, I switched to NTFS for the external SSD, now it is slightly slower compared to windows, but fast enough

I run FFS 14.0 donation on a Win 11 Pro with an internal Samsung 990 Pro and external Samsung T9 with special cable and USB C 3.2
FFS ist extremly fast. It takes seconds to compare a million files, and seconds to copy 10 thousands of files.
that is incredible !!

with dual boot on the same machine, ubuntu 24.04.2 LTS, the same job takes about 5 Minutes to compare only 500.000 files, the top window showing the progress of files shows the files on the usbdrive (internal drive is fast)
playing with threads makes no difference, afterwards copy is quite fast,
I have to adjust the directories for the usb drive: instead of [T9] on Windows I use /media/xxx/T9 on ubuntu
filesystem is exfat
read with lsusb
Bus 002 Device 002: ID 04e8:61fd Samsung Electronics Co., Ltd PSSD T9
Bus 002.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/5p, 20000M/x2
|__ Port 001: Dev 002, If 0, Class=Mass Storage, Driver=uas, 20000M/x2

I don't know what to do

[Lonewoolf]

Since a few weeks i have the same problem, only 25kb/s.
After days of trial and error i found out, that the problem is Malwarebytes.
Disabling this AntivirusTool and go back to Win Defender, now it runs with 110MB/s.
Maybe the Truetime-Protection of Thirdparty Tools is the problem.