Btrfs RAID-10 performance

[Sami Ketola]

> On 7. Sep 2020, at 12.38, Miloslav Hůla <miloslav.hula at gmail.com> wrote:
> 
> Hello,
> 
> I sent this into the Linux Kernel Btrfs mailing list and I got reply: "RAID-1 would be preferable" (https://lore.kernel.org/linux-btrfs/7b364356-7041-7d18-bd77-f60e0e2e2112@lechevalier.se/T/). May I ask you for the comments as from people around the Dovecot?
> 
> 
> We are using btrfs RAID-10 (/data, 4.7TB) on a physical Supermicro server with Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz and 125GB of RAM. We run 'btrfs scrub start -B -d /data' every Sunday as a cron task. It takes about 50 minutes to finish.
> 
> # uname -a
> Linux imap 4.9.0-12-amd64 #1 SMP Debian 4.9.210-1 (2020-01-20) x86_64 GNU/Linux
> 
> RAID is a composition of 16 harddrives. Harddrives are connected via AVAGO MegaRAID SAS 9361-8i as a RAID-0 devices. All harddrives are SAS 2.5" 15k drives.
> 
> Server serves as a IMAP with Dovecot 2.2.27-3+deb9u6, 4104 accounts, Mailbox format, LMTP delivery.

does "Mailbox format" mean mbox?

If so, then there is your bottleneck. mbox is the slowest possible mailbox format there is.

Sami