EXT4/LVM recommendations for 3TB of mdbox ?

Nicolas C dovecot at nryc.fr
Wed Jun 24 21:41:28 UTC 2015

Le 24/06/2015 22:35, dmiller at amfes.com a écrit :
> On 2015-06-24 13:03, Nicolas C. wrote:
>> Hello,
>> Do you have recommendations on EXT4 and LVM options for a 3TB
>> file-system for mdbox?
>> We currently use the mbox format on a XFS with poor performances since
>> the update in v2.1 (Debian).
> What qualifies as "poor performance"?

Way more i/o for the exact same conditions.

We kept dovecot in version 1.2 on Wheezy (with pinning) and it was 
running fine but as soon as we installed the official Wheezy version of 
Dovecot (2.1) the iowait increased on the server.

> How many users?

"doveadm who -1" reports an average of 4.000 connections during business 
hours with peaks going up to 6.000.

>> We will switch to EXT4 to have the possibility of shrinking the
>> file-system if needed (which is not possible with XFS), we currently
>> have LVM partitions but with mdbox we will use LVM snapshots to backup
>> the server in a consistent state.
>> So,
>>  - any particular options to use with mkfs.ext4 for the creation of
>> the FS ?
> It's not what you asked - but the options for XFS creation and mounting
> can make a fair bit of difference.

Yes, I saw the "XFS vs EXT4 for mail storage" thread (2013) and I was 
wondering if, since then, people had a feedback on EXT4.

>>  - do you recommend a «thin» logical volume ? Our storage (IBM
>> Storwize v7000) already have thin provisioning capabilities.
>> The server will be a VMware virtual machine running Debian with RDM
>> LUNs of 500GB. Data blocks will be automatically spread across several
>> RAID disk (SSD, SAS, SATA) by the v7000. The «mdbox_rotate_size» will
>> be configured around 10MB.
> I happen to be using 32MB.
> Just going to mdbox can make a measurable performance increase.  I also
> make use of single-instance-storage.

We know that mdbox will be helping, we are very eager to get rid of the 
old mdbox format!

> Everyone is going to have their own opinions and experiences with
> filesystems.  I personally have had mixed issues with EXT3/4 but have
> enjoyed great success with XFS.  Admittedly my server is probably much
> smaller than others but I still need to depend on it.

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