Having had a week with the system I'm now inclined to believe that the issues I've seen are not necessarily related to SIS and zlib but may be due to replication instead.
After experiencing these issues and looking at historical mailing list posts I wrote a basic script (as was suggested as a possible diagnostic approach for SIS before SIS was even implemented!) which pulled all the mail from a user
doveadm fetch -u username body all > /dev/null 2>error.log
This generated errors in error.log for every e-mail with a problem. From that and some use of sed,uniq,cut and ln I was able to (re)create the missing links. Unfortunately the error generated was only the first missing link for all the links expected for an e-mail. So my script had to be run multiple times per user until no more errors were reported. This wasn't all that onerous given I was basically running on a test box before mass migrating my users. A better approach would have been to scan the mdbox files for all links expected and check the existence of them all.
Having (re)created all missing links I've not had a single instance of a link being missing after a week of delivery of mail (where the errors were regular before this procedure).
I have also since looked at how replication handles links. What I hadn't expected was that the links created on the server pair are not the same. Although I had two servers which started in the same state (one a clone of the other) after a month or so of replication they had diverged to the state where if I sent a test message to the one server I could see the file name of the link created to the has was not the same on both servers (although obviously the hash itself was the same name and content wise). This leads me to believe the errors I saw where most likely down to my expecting the two servers in the pair to have identical SIS attachment directories/hardlinks to hashes and the way I handled my migration. Coming from a database mail server were replication master/slave means the backend should be absolutely identical if all is working I may simply have gotten the wrong idea of dovecot replication.
With my 2.3.1 and 2.3.4 replication pair there were a lot of the tcp errors which the changelog for Dovecot stated had been fixed post 2.3.1; mainly the connection timing out after 10 minutes.
Looking at the code for replication (which I'm not going to claim I've fully go to grips with) it looks like the name of a hardlink is made up of essentially [hash]-[identifier including mailbox GUID]. It must be the case then that the [identifier including mailbox GUID] can diverge between server pairs, at least with 2.3.1 as a version involved.
Errors with missing links to files when using Single Instance Storage and zlib (Dovecot 2.3.4)
*Daniel Schütze*daniel at cwa.uk.commailto:dovecot%40dovecot.org?Subject=Re:%20Re%3A%20Errors%20with%20missing%20links%20to%20files%20when%20using%20Single%20Instance%20Storage%0A%20and%20zlib%20%28Dovecot%202.3.4%29&In-Reply-To=%3Ccc3b8bf3-055f-6908-95a0-d337544a8998%40cwa.uk.com%3E /Tue Dec 18 15:39:41 EET 2018/
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I'm running Dovecot 2.3.4 with Single Instance Storage (SIS) and zlib and I am frequently seeing errors where files are missing in the attachments directory even though the zipped file in the hash directory is actually there. This appears not to have been an issue in Dovecot 2.3.1 Requested output of the server below.
The error looks like this in the log
Dec 18 08:58:58 dovecot01 dovecot: imap(username)<3692><RKnPGEh9fC3AqAAB>: Error: Mailbox INBOX/FOLDER: UID=41: read(attachments-connector(zlib(/usr/home/vmail/mail/username//mdbox/storage/m.411))) failed: read(/usr/home/vmail/attachments/91/08/91085773a0774909207852b8f9c98dbe22fe5a31-e88ba0276aae135cd2050000d09efc50[base64:19 b/l]) failed: open(/usr/home/vmail/attachments/91/08/91085773a0774909207852b8f9c98dbe22fe5a31-e88ba0276aae135cd2050000d09efc50) failed: No such file or directory (FETCH BODY[])
I'm also seeing errors when replication fails
dovecot: dsync-local(username)<bzg3MqjhGFxmFwAAzRvpBw>: Error: dsync(servername): read(attachments-connector(zlib(/usr/home/vmail/mail/username//mdbox/storage/m.413))) failed: read(/usr/home/vmail/attachments/45/42/4542dcf385f6b4a4dc8752b96db1d7ad8a8023d5-ac735007f6bd135c93440100cd1be907[base64:19 b/l]) failed: open(/usr/home/vmail/attachments/45/42/4542dcf385f6b4a4dc8752b96db1d7ad8a8023d5-ac735007f6bd135c93440100cd1be907) failed: No such file or directory (last sent=mail, last recv=mail (EOL))
It is not the case that every replication fail has a corresponding imap access fail.
I am running Dovecot 2.3.4 on FreeBSD11.2 and I did not see this error on Dovecot 2.3.1 FreeBSD 10.4. Both installs had the same configuration for Dovecot. Both installs were made from source code and not packages (as the need for the non standard fts and mysql options).
During my testing I had the 2.3.1 install receive mail and replicate to the 2.3.4 and that was working fine (except for tcp connection issues which I saw was fixed in the changelog).
Unfortunately having gone into testing with real account and mail being sent to the 2.3.4 install I'm seeing the above errors.
My clients are using Thunderbird on desktops and Roundcube for webmail.
My users report they can see the e-mails fine in their webmail (Roundcube) and only Thunderbird is giving issues. I admit I don't know how this can be the case as both systems use the same account details.
In everycase so far there is a file in the hashes directory I have hand crafted the missing file (i.e. link) using ln and this restores access in Thunderbird.
Clearly this is an big issue for my install and I'd appreciate any help!
At the moment it looks like my course will be to try and script creation (recreation?) of the links from the error logs (I've seen people talking about this online) but that isn't really what I'm after.
DOVECOT CONFIG
# 2.3.4 (0ecbaf23d): /usr/local/etc/dovecot/dovecot.conf # Pigeonhole version 0.5.4 (60b0f48d) # OS: FreeBSD 11.2-RELEASE-p5 amd64 # Hostname: dovecot01.cwa.uk.com dict { acl = mysql:/usr/local/etc/dovecot/dovecot-dict-sql.conf.ext } disable_plaintext_auth = no doveadm_password = # hidden, use -P to show it first_valid_uid = 145 last_valid_uid = 145 mail_access_groups = mail mail_attachment_dir = /usr/home/vmail/attachments mail_attachment_min_size = 64 k mail_gid = vmail mail_location = mdbox:~/mdbox:INDEX=/indexdisk/indexes/%n mail_plugins = " fts fts_solr acl zlib notify replication" mail_privileged_group = mail mail_uid = vmail managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext namespace { list = yes location = mdbox:%%h/mdbox:INDEXPVT=~/mdbox/shared/%%n prefix = shared/%%n/ separator = / subscriptions = yes type = shared } namespace inbox { inbox = yes location = mailbox Drafts { auto = subscribe special_use = \Drafts } mailbox Junk { auto = subscribe special_use = \Junk } mailbox Sent { auto = subscribe special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { auto = subscribe special_use = \Trash } prefix = type = private } passdb { args = /usr/local/etc/dovecot/dovecot-sql.conf.ext driver = sql } plugin { acl = vfile acl_shared_dict = proxy::acl fts = solr fts_autoindex = yes fts_solr = url=http://localhost:8983/solr/dovecot/ mail_replica = tcp:192.168.0.138:12345 replication_dsync_parameters = -d -l 30 -U sieve = ~/.dovecot.sieve sieve_dir = ~/sieve sieve_duplicate_default_period = 1h sieve_duplicate_max_period = 1d sieve_global_dir = /usr/home/vmail/sieve/global/ sieve_global_path = /usr/home/vmail/default.sieve sieve_vacation_default_period = 1d zlib_save = gz zlib_save_level = 6 } protocols = imap sieve service aggregator { fifo_listener replication-notify-fifo { user = vmail } unix_listener replication-notify { user = vmail } } service auth { unix_listener auth-userdb { mode = 0777 } } service dict { unix_listener dict { mode = 0600 user = vmail } } service doveadm { inet_listener { port = 12345 } } service replicator { process_min_avail = 1 unix_listener replicator-doveadm { mode = 0600 user = vmail } } ssl = no userdb { driver = prefetch } userdb { args = /usr/local/etc/dovecot/dovecot-sql.conf.ext driver = sql } protocol lda { mail_plugins = " fts fts_solr acl zlib notify replication sieve" submission_host = 192.168.0.1:25 } protocol imap { mail_plugins = " fts fts_solr acl zlib notify replication imap_acl imap_zlib" }
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