[Dovecot] index IO patterns

[Stan Hoeppner]

On 5/12/2012 2:26 AM, Cor Bosman wrote:

> The indexes are doing a lot of iops on the metrocluster, and it's a bit
> of an expensive option for something it's not even that good at. 

This clears things up a bit.

> Im aiming for something with 2 servers, each with a 12 disk enclosure
> with SSD for fast random io with 10G network interfaces, 24 core, 48GB
> memory. 

AMD is a great platform and I laud your preference for it.

> I just want to test some io patterns on different hardware/software
> solutions, including the metrocluster itself, before we commit to
> a specific solution. Im slightly leaning towards DRBD right now.

A DRBD cluster simply doubles your costs--twice the disks/enclosures,
twice the servers, and adds another layer of redundancy software to the
storage stack.  It can be even more if one decides to cluster 3-6 or
more DRBD servers.

Have you considered something like a Nexsan E18?  In 2U it gives you
dual PSUs, dual active/active RAID controllers each w/ 2GB BBWC, 2x8Gb
FC and 2x1GbE iSCSI ports per controller.  Optionally you can replace
the FC ports with the same number of 10GbE iSCSI ports.  It offers up to
18 100/200/400GB SLC SSDs, or up to 36/78 of these SSDs w/the E18X or
E60X expansion chassis.

http://www.nexsan.com/en/products/e-series/~/media/Nexsan/Files/products/e-series/library/NexsanESeriesDSpdf.ashx

http://www.nexsan.com/en/products/e-series/tech-specs.aspx
http://www.nexsan.com/products/e-series.aspx

You'd simply create a single RAID1+0 array of all 18 SSDs, export it as
a LUN on each iSCSI port, configure SCSI multipath and the iSCSI
initiator on each Dovecot host, install GFS2/OCFS2, format the LUN and
go.  With 18x200GB SSDs you'll get 1.8T of net capacity and well north
of 100K sustained real world random r/w block IOPS.  And without needing
two beefy dual socket AMD server chassis mirrored with DRBD.  And of
course you'll still want to use Dovecot Director to avoid locking issues.

Contact the Nexsan European office to see about an evaluation unit:
http://www.nexsan.com/about/contact/locations.aspx

Disclaimer:  I've never worked for Nexsan nor any affiliate.  I'm simply
a past customer very satisfied with their products and philosophy/strategy.

-- 
Stan