Error Code: -24 Server Busy. Too Many Connections

English Backup and data protection
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1

Hi everyone,

I am receiving this error causing a backup to fail and I could use some help:

[Hybrid Backup Sync] Failed to complete Sync job: “Server2 to Server1”. Server busy. Too many connections. Wait, and try again later. Error code: -24

I can’t seem to figure out why this error code is coming up and wanted to see if anyone has any information on where to look or how to troubleshoot this. The error code happens every time a backup is scheduled to occur using Hybrid Backup Sync 3. HBS3 works fine backing up to two other harddives we have, so I’m not currently out any data, but I hadn’t experienced any errors with Server2 up until April 2nd, and I’ve been looking into this as I am able. The internet doesn’t have much on error code -24.There do not appear to have been any updates on April 2nd for the QNAP firmware or HBS3 software.

I have tried getting to /share/CACHEDEV1_DATA/.@qsync/detail-logs via SSH, though the admin doesn’t appear to have sufficient permissions to view this location. I don’t even know if the logs here would yield results which differ from the typical HBS3>Debug Report via the AppCenter, so logging in via SSH might not be necessary.

Any ideas on what could cause a server to be busy? There’s only one wired connection between the two servers. My only suspicion is that Server1 is relatively close to its storage threshold (8.88TB of 10.69TB), however I have Server1 rigged to alert me when that threshold is reached and I have yet to be notified.

Sending NAS
Operating System of PC: Windows 10 19045.5737 - Connecting via web login to server
NAS Model: TS-873A
QTS Version: 5.2.3.3006 (2025/01/08)
Network Setup: Single Port, I believe

Receiving NAS
Operating System of PC: Windows 10 19045.5737 - Connecting via web login to server
NAS Model: TS-469U
QTS Version: 4.3.4.2814 (2024/06/18)
Network Setup: Single Port, I believe

Thank you!

2

try SSH to your NAS. then run:

netstat -an | grep ESTABLISHED

this shoudl list what is connected to the NAS and what ports are being used.

did you try stopping and starting HBS3 on the NAS and see if that dropped any connections?

3

Thank you!

I did try stopping and restarting HBS3 in order to see if the time of day had anything to do with the syncing error, yes, and unfortunately I was able to trigger the error during the day. Our backups are normally set up to sync in the evenings when traffic is low, though there may still be connections to the server (even if I try to discourage it :slight_smile: )

Would I want to check connections against both servers since Server1 is what cannot be connected? Server2 spits out 24 lines using the netstat code that appear in this format:

tcp 0 0 [server ip address]:445 [local ip addresses]:[five digit port] ESTABLISHED

The bottom 6 addresses look kind of like ipv6 addresses, but they contain 8080 ports of our server IP address followed by my local PC IP address. (Edit: Finding these are my current connection to the server via web)

Only oddity I’ve noticed is that there’s a ‘64’ in the second digit column after ‘tcp’ and a port 22 on the same line of one of our connections, which looks to be traced back to my computer. (Edit: Finding this is the SSH into the NAS)

Edit 2: I see now. Thank you for steering me in the right direction, Toxic. Server1 has about 1000 loopback addresses which I can only imagine are the “connections” preventing the backup from occurring. Running HBS on Server2 to try to sync with Server1 doesn’t drop any connections. Looking into it from here

Thanks for the tips!