Thanks for the report. It looks like chunked uploading was completely broken by recent backend changes. We'll look into it. In the meantime, please disable the experimental chunked uploading user preference when using Upload Wizard.

(In reply to comment #0)

Created attachment 11080 [details]
(c) by ForestWander

I have 2 files (not more tested yet) and chunked upload always fails with:

<?xml version="1.0"?><api servedby="srv298"><error
code="internal_api_error_MWException" info="Exception Caught: Stashing
temporary file failed: UploadChunkFileException error storing file in
&#039;mwstore://local-multiwrite/local-temp/7/7a/20120906101442!php6Ih8HM.jpg&#039;:
backend-fail-synced;
mwstore://local-multiwrite/local-temp/7/7a/20120906101442!php6Ih8HM.jpg"
xml:space="preserve" /></api>

No matter whether I use my bot (self written) or UploadWizard.

Does this still occur?

Attached:

(In reply to comment #2)

Does this still occur?

I've not checked the same thing, but as I mentioned on bug 40114 just this morning uploading some 4 MiB files failed with a bunch of internal_api_error_MWException before I disabled chunked uploading.

One problem was fixed in https://gerrit.wikimedia.org/r/#/c/23241/.

Sorry for my last comment; as for the last update, I tried again my 20 4 MiB images and none failed. I also tried a 200 MiB DjVu: the upload was very slow (oscillating 100-200 KiB/s) and didn't seem to fail with this bug but ended with internal_api_error_UploadStashFileNotFoundException (the usual one).

Yes, fixed, thanks.