On 8. Sep 2020, at 12.35, Robert Nowotny <rnowotny1966@gmail.com> wrote:

Dear Aki,
I switched to "gz" now, since "zstd" also gave some errors on writing to files.

What kind of errors?

Probably this? :

Panic: file ostream.c: line 287 (o_stream_sendv_int): assertion failed: (!stream->blocking)

can be - unfortunately I do not have the log files anymore...

Sep 3 08:33:25 lxc-imap dovecot: imap(mpaul)<48684><2/9E5mKuAezAqKjk>: Error: Mailbox Sent: UID=2171: read(zlib(/home/vmail/virtualmailboxes/mpaul/storage/m.119)) failed: read(/home/vmail/virtualmailboxes/mpaul/storage/m.119) failed: Broken pipe (FETCH BODY[])

Also this way you can see if the broken mail is actually xz or zstd or zlib. It would be nice to know if there are any zstd or zlib compressed mails that have problems. We did a lot of stress testing with zstd and also with xz, but haven't been able to reproduce any problems. It's also strange that it says taht the error is "Broken pipe" - that doesn't indicate that the mail is corrupted but that there is something more strange going on. So perhaps you don't actually have any mails written as corrupted, but Dovecot is just somehow having trouble reading the mails.

I managed to reproduce this. The files aren't corrupted, it's just that reading is failing. The attached patch should fix the xz code and should make your files readable again.

Yes, it works ! I switched now to "zstd" compression and currently re-compressing all user imap folders (one by one)

thank You so much !

Robert