Hello
Am 09.10.2014 um 20:41 schrieb Urban Loesch:
Hi,
Am 09.10.2014 12:35, schrieb Martin Schmidt:
Our MX server is delivering ca. 30 GB new mails per day.
Two IMAP proxy server get the connections from the users. Atm.
without dovecot director.
We've got around 700k connections per day (imap 200k / pop3 500k)
Are this the hole connections per day? How many concurrend connections
do you have at the same time on each server?
we've got 3 Fileserver with ca. 1200 concurrend IMAP connections and ca.
50 concurrend POP3 connections on each server.
So we want to make a new system.
We desire the new system to use mdbox format ( bigger files, less I/O)
and replication through dovecot replication (active/active) instead
of drbd.
I have no experience with dovecot replication (Still on our roadmap).
We are currently using drbd on a 10Gbit dedicated link. Works very
well for us.
Each fileserver should know every mailbox/user and for the time being
2 dovecot proxies for the user connections (IMAP/POP).
(later after the migration from the old system to the new, dovecot
director instead of proxies, for caching reasons).
As Florian said, enable zlib. This also decreases I/O, but needs a bit
more of CPU. But not that much.
Yes we have enabled it, estimated space saving is up to 40%
we've got 2 new fileservers, they have each SSD HDDs for "new-storage"
and 7200rpm SATA HDDs on RAID 5 with 10 TB for "alt-storage"
32 GB RAM per Server
You also could move the INDEX files from mdbox to different SSDs. We
are doing so with 40k accounts and 2TB user data. Index partition has
only 22GB used and is increasing not very fast.
On our testsystem we've got it also on a raid 1 SSD, only alt-storage is
on raid 5. Looks good.
Do you have some tips for the system?
Do you believe 32 GB RAM are enough for one fileserver each and have
you experience with the I/O Waiting problem with huge amounts of Data
on the alt-storage?
Could there be issues with the RAM, if one fileserver has a downtime,
so the second one has to take over all mailboxes for a short amount
of time?
I think memory is not the problem. On IMAP/POP3 servers the main
problem is I/O. But with dovecot mdbox and index files on SSD's we
have no problem at the moment.
On each of our 3 Fileserver we've got 16 GB RAM, 5-7 GB is used and rest
is cached. You might be right, the i/o is always the bottleneck.
In general are only 2 new fileserver enough or should we think in
bigger dimensions, like 4 fileserver
Storage expansion in the new servers should not be a problem (bigger
HDDs and a few slots free, so we can expand the raid 5).
We are using raid 10 hardware raid controller with cache and sata
7200rpm disks. OK, raid 10 needs more disks, but is much faster than
raid 5. Raid 5 is not very fast in my eyes.
We've made tests with raid 10 and raid 5, on 4 sata 7200rpm disks, of
course raid 10 was faster, but overall not very much. And you can expand
raid 5 easier.
Can you tell me, if you have a high "Waiting" on your alt-storage?
thank you
kind regards
Martin Schmidt
Regards
Urban
Thank you for your impressions.
kr
Martin Schmidt
