doveadm backup mdbox - initial copy slow

[Aki Tuomi]

On 30.8.2019 12.33, Gerald Galster via dovecot wrote:
> Hello,
>
> when calling doveadm backup like in the following example, it seems to flush every email to disk
> maxing out harddrives (iops) and resulting in very poor performance:
>
> Calling doveadm -o plugin/quota= backup -u "statusmails at domain.com" "mdbox:/backup/vmail/domain.com/statusmails"
> finished in 212 secs [changes:1800 copy:1800 delete:0 expunge:0]
>
> The source mdbox holds 1800 small emails and uses about 20 MB disk space only.
>
> I've tried -f (full sync) and -l 30 (locking the mailbox) which did not get faster, nor did doveadm sync -1.
>
> When using doveadm import all mails are copied in less than 3 seconds:
> time doveadm -o mail=mdbox:/backup/vmail/domain.com/statusmails import mdbox:/var/vmail/domain.com/statusmails "" all
> real	0m2.605s
>
> Are there any other options I could try to speed up doveadm backup, avoiding the flush after each email?
>
> This is doveadm from dovecot 2.2 (>= 2.2.33). Does anyone get better results with 2.3 tree?
>
> Best regards
> Gerald

Try setting mail_fsync=never

Aki