Connection Error with USB-Device

[GrafZahl]

I am running a PVE on a HP Microserver Gen 10+.
To run daily backups I am running a PBS inside a VM on the PVE. As backup-storage I use an external USB-harddisk which is passed into the PBS with USB-passthrough.
As I also need USB on the host I can not PCI-passthrough the USB-controller.
I also need all SATA-Ports ob the PVE.
On the external USB-drive is an ext4 partition ontop a luks-layer. It is USB3-chassy with a Seagate Ironwolf HDD.

It is running, but when doing backups I get "connection errors" in the PBS like the following:


```
2026-03-08T18:18:20+01:00: starting new backup reader datastore 'externes_backup_1_crypt': "/mnt/datastore/externes_backup_1_crypt/ds1"
2026-03-08T18:18:20+01:00: protocol upgrade done
2026-03-08T18:18:20+01:00: GET /download
2026-03-08T18:18:20+01:00: download "/mnt/datastore/externes_backup_1_crypt/ds1/ns/minipve/ct/116/2026-03-03T03:24:04Z/root.mpxar.didx"
2026-03-08T18:18:20+01:00: register chunks in 'root.mpxar.didx' as downloadable.
2026-03-08T18:18:20+01:00: GET /chunk
2026-03-08T18:18:20+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/b1ce/b1ced323115b3659cde78dd3762ce29624baffde3af0093614b1a18a2a0ff490"
2026-03-08T18:18:20+01:00: GET /chunk
2026-03-08T18:18:20+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/dda9/dda977da581476d3f75f9a5db2259acbc33a159a453da9946b34ec9d64457e79"
2026-03-08T18:18:36+01:00: GET /chunk
2026-03-08T18:18:36+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/2a7f/2a7f1d17e4ca4a86234f595ed3c3c473540425c79492eb663ab292df5aa3d90c"
2026-03-08T18:18:57+01:00: TASK ERROR: connection error: not connected
```

```
2026-03-08T18:00:50+01:00: starting new backup reader datastore 'externes_backup_1_crypt': "/mnt/datastore/externes_backup_1_crypt/ds1"
2026-03-08T18:00:50+01:00: protocol upgrade done
2026-03-08T18:00:50+01:00: GET /download
2026-03-08T18:00:50+01:00: download "/mnt/datastore/externes_backup_1_crypt/ds1/ns/minipve/ct/101/2026-03-03T03:00:30Z/root.mpxar.didx"
2026-03-08T18:00:50+01:00: register chunks in 'root.mpxar.didx' as downloadable.
2026-03-08T18:00:51+01:00: GET /chunk
2026-03-08T18:00:51+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/ad31/ad31965081c72caccea9ef3ce2ddabd43da015664feedd53b5b3fa01e06ce237"
2026-03-08T18:00:51+01:00: GET /chunk
2026-03-08T18:00:51+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/4d30/4d30b4f319c858a9b14679710bf20f381d1e21b731f296eef77584b4eade869b"
2026-03-08T18:00:51+01:00: GET /chunk
2026-03-08T18:00:51+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/efbf/efbfbe981c65b6285385ef883c7ee53e8ec4493d08f38f9ffd1dd3336930b8e9"
2026-03-08T18:00:51+01:00: GET /chunk
2026-03-08T18:00:51+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/ac9f/ac9f8bf6dda442134fff832677d7b227aa8a5f09eeaeddc61babc74bd762a2c1"
2026-03-08T18:00:52+01:00: GET /chunk
2026-03-08T18:00:52+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/bd5f/bd5ff7395abe8254f58540503ed01daced331592a44d4b4cb6136d34ecbacf2f"
2026-03-08T18:00:52+01:00: GET /chunk
2026-03-08T18:00:52+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/b026/b0266495deebf169204d0c4afe19d268a782b738cf89e4221d3503eed735ef73"
2026-03-08T18:00:53+01:00: GET /chunk
2026-03-08T18:00:53+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/63c8/63c8bcaa415b983adab22a7935753d242a03eaedb6497ca97e4bf799fb480b3e"
2026-03-08T18:01:00+01:00: GET /chunk
2026-03-08T18:01:00+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/8c7c/8c7c1a9da00d784a63a6b53f7f47104a9ea0927db4ff3a29e9aaeb83902ed3c6"
2026-03-08T18:01:00+01:00: GET /chunk
2026-03-08T18:01:00+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/4b89/4b894e7c11f384bd3d147b6c447b959e8d0369f12fcda672b2d9c87ad251652f"
2026-03-08T18:01:04+01:00: GET /chunk
2026-03-08T18:01:04+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/6de5/6de5a7bf51d0ea6e4f72dcffa93b357df2039790a16fe3f1518ec3a1e4c1b30d"
2026-03-08T18:01:06+01:00: GET /chunk
2026-03-08T18:01:06+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/16e5/16e5494f9a6be206ba0e8d45685ff3f057b8898baf10d61e6efea5b8647e7816"
2026-03-08T18:01:07+01:00: GET /chunk
2026-03-08T18:01:07+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/86c9/86c9a48bdffee7bb3b0832099063f3f3a72b53d99b12ec36456eb675ab5a75d3"
2026-03-08T18:01:07+01:00: GET /chunk
2026-03-08T18:01:07+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/0a14/0a14f88864f7f1a1f53417e9631c6ee1e9ef52dda23d037fd5cc36418214c718"
2026-03-08T18:01:08+01:00: GET /chunk
2026-03-08T18:01:08+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/bcac/bcaced26f90cb26dc34b714001910272db286075037c78e18c7b3e42ad93be2f"
2026-03-08T18:01:09+01:00: GET /chunk
2026-03-08T18:01:09+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/caf6/caf6b9b9c93de4eef8859d4492a910f6ee3ee633745c7e31da1a5ee84bd65fe0"
2026-03-08T18:01:10+01:00: GET /chunk
2026-03-08T18:01:10+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/df17/df178f71510e9db9c55361ee2063a7f6b8a21591a728476f1ea12e9e7e9ceafe"
2026-03-08T18:01:11+01:00: GET /chunk
2026-03-08T18:01:11+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/aeda/aedab9860d54941383e962c34f8df9c254c875036101d761b797dac3a27de0be"
2026-03-08T18:01:46+01:00: GET /chunk
2026-03-08T18:01:46+01:00: download chunk "/mnt/datastore/externes_backup_1_crypt/ds1/.chunks/71ef/71ef89c5a319f389f056335ee33182754381193cac910ff350bc0bfca4002e19"
2026-03-08T18:02:47+01:00: TASK ERROR: connection error: not connected
```

I already switched to another USB-chassy and another power supply

At next I mounted the external drive on the PVE and did a virtiofs-directory-passthrough. But with the same errors.

I have no good ideas what else could cause the problems. Can anyone help?

I know this is not recommended. I know the backup has no redundancy. It's not the only backup I have.

 

[DerekG]

The USB ports in these older system are notoriously unreliable, and using that for PBS which is a heavy on the I/O appliance is really asking for trouble.
In addition to that using a spinning disk as your backup data store is also a problem due to the heavy I/O loading. I think that Proxmox recommend SSD (but it's been a while since I checked that).

The only way I've found to reliably use USB drives on my Intel 6th Gen mini PC's was to utilise an OMV VM and then create network shares, but in your case that will also be a problem for connecting a PBS data store to one of those shares.

 

[GrafZahl]

Hey there,
sorry for my really late reply but I was busy. But I could test several things about this problem.
What I have done:
- I tried several HDDs
- I tried several external USB enclosures
- I used the internal USB-port and tried using a pcie-USB-card.
- I installed pbs directly onto the machine, parallel to pve.

All of those did not change the situation.

- Plugging the datastores to an other pbs worked and I could run the backups on it without issue... Only if the external HDD is on this HP machine brought this errors.
- The backus are OK, and I could verify them... But those errors...

Now I found that only CTs are affected by this issues. VMs are backed up without this message.

Now I changed the "PBS change detection mode" from "Metadata" back to "Default" and: NO ERRORS!
Now my backups need over 5 hours instead of 25 minutes, but therefore I do not get those annoying errors.

I first thought it could be, because I use mountpoints in the CTs, but even CTs without mountpoints showed these errors. So I don't get the issues. But it seems to, that Metadata-mode makes something my machine does not like if doing backups on the same hardware.

Running backups of those CTs to the same datastore, but connected to another hardware with a PBS worked flawless when using Metadata-mode.