I have installed Ubmbrel on to a Dell Optiplex 7040. The machine is an i5 processor with 32G RAM and a 2 TB NVME M.2 SSD.
The operating system has loaded successfully and I have been able to install Bitcoin Coin and start it syncing. However, it will not Sync past 7% of the block chain. When it crashes I get the following errors:
2025-10-27T08:55:05Z [error] Deserialize or I/O error - ReadCompactSize(): size too large: iostream error at FlatFilePos(nFile=275, nPos=93274100) while reading block
2025-10-27T08:55:05Z [error] A fatal internal error occurred, see debug.log for details: Failed to read block.
2025-10-27T08:55:05Z [error] ProcessNewBlock: ActivateBestChain failed (Failed to read block.)Error: A fatal internal error occurred, see debug.log for details: Failed to read block.
When I restart the sync, it goes back to around 5% but crashes again at around 7%.
So two things you can try for this. If you have no funds or wallet linked to it you can just uninstall and reinstall the app and that should fix it. Otherwise follow the instructions here Bitcoin core stopped unexpectedly - #3 by Lastgameforlife .
Thanks for your reply. I did uninstall Bitcoin Core and thought I’d give Bitcoin Knots a try. The same issue occurred again with Knots.
Given that the error appears to relate to the size of the block being to large, actually doubled the capacity of the send and receive buffers to see if that would help. That didn’t appear to help as the same error occurred on the next attempt.
I have uninstalled Knots and re-installed Core and will give that a go again. If that fails, I’ll try the re-indexing approach.
I have followed the previous advice provided as well as uninstalling and re-installing the App, I have also replaced my 4TB SSD with a 2 TB SSD and re-installed the Umbrel Operating System. Yet still, I cannot load more than 8% of the blockchain without the Bitcoin App stopping with fatal errors. Adding reindex=1 to the overrides does not seem to have any effect.
There appear to be 2 flavours of error:
2025-10-30T06:07:27Z [error] Deserialize or I/O error - ReadVarInt(): size too large: iostream error at FlatFilePos(nFile=392, nPos=132725) while reading block undo
2025-10-30T06:07:27Z [error] A fatal internal error occurred, see debug.log for details: Failed to read undo block data 000000000000000002a8834e463171f86c0fb02c72a4d4db1d689b65bd7d93f6 from disk
Error: A fatal internal error occurred, see debug.log for details: Failed to read undo block data 000000000000000002a8834e463171f86c0fb02c72a4d4db1d689b65bd7d93f6 from disk
2025-10-28T21:36:14Z Fatal LevelDB error: IO error: /data/bitcoin/indexes/blockfilter/basic/db/000004.log: Bad message
2025-10-28T21:36:14Z You can use -debug=leveldb to get more complete diagnostic messages
2025-10-28T21:36:14Z
EXCEPTION: 15dbwrapper_error
Fatal LevelDB error: IO error: /data/bitcoin/indexes/blockfilter/basic/db/000004.log: Bad message
bitcoin in scheduler
EXCEPTION: 15dbwrapper_error
Fatal LevelDB error: IO error: /data/bitcoin/indexes/blockfilter/basic/db/000004.log: Bad message
bitcoin in scheduler
terminate called after throwing an instance of ‘dbwrapper_error’
what(): Fatal LevelDB error: IO error: /data/bitcoin/indexes/blockfilter/basic/db/000004.log: Bad message.
I am at a loss to determine how to resolve these issues other than to downgrade to a previous version of the App and/or the operating system or both. (If that is possible ?)
Any assistance would be greatly appreciated as I have been trying to complete this installation for 7 days now.
I had a bad experience with Dell hardware running Core and Knots in the past. After discovering some documented issues with Dell hardware running nodes, I ditched the Dell and went with Lenovo. No problems since. Find a cheap ThinkPad like the 11e, i490, T470s etc. They are bulletproof.
I must thank you for your assistance and am most grateful for it but given oztayls following post, it looks like we’re flogging a dead horse. Although I believe there are work arounds possible from what I have found also found out, there is no point building something on a flawed foundation.
I have to say this is Murphy’s Law in it’s purest form. I chose to use the only PC highlighted in a number of forums as being the only one that won’t work with Umbrel and some other nameless competitors.
I have to agree, the Lenovo products are pretty bullet proof, in fact I’ve seen one survive a motorcycle crash ! Unfortunately I no longer work for IBM, so my access to them is limited but I’ll see if my former colleagues can point me to a recycler
At this stage though, the plan moving forward is to gut the evil Dell and rebuild it on a Gigabyte board that I happen to have on hand. It will be a bit of a bigger footprint but should not have the BIOS issues associated with the Dell 7040 machine.
Thank you both for your assistance, I will update this post with my progress
I just finished installing in a similar system. You’re gonna have to Prune like mad. I don’t kow if that;s causing the errors, but I pruned bitcoin Node and Knots to 750gb each and Libre relay to 200gb and I got it all synced - but have only 102GB left on a 2TB drive. the 32GB ram is good as I saw up to 24gb used when syncing
Apologies for the delay in progressing this issue, unfortunately life got in the way.
So, I gutted the Dell and transplanted the the components on to a Gigabyte GA-Q170M-MK motherboard.
Everything fired up and was running just fine. I loaded Umbrel OS and upgraded it to version 1.5. Then I loaded Bitcoin Knots and started the synchronisation process.
I couldn’t believe it when the sync crashed at 2% ! I checked the logs and it appeared to be the same issue as previous. I removed Knots and loaded Bitcoin Node. This time I got to 3%. I then repeated the process with a different NVMe drive, with the same results.
After reviewing the logs, I felt that the issue was actually NVMe drives’ I/O failing and causing the problem. I made a quick trip to the computer store and bought a new, higher quality 4TB NVMe drive.
I installed the new drive and loaded it up and started syncing Bitcoin Node. Fourteen hours later I had a fully synced node !
Yes, I was always nervous about using a 2TB drive and opted for the 4 TB instead. According to Bitcoin node the space used by the blockchain is 799 GB on my machine. I have yet to add other apps which I’m sure will eat into the remaining capacity. Thanks for the heads up on this.
