hardware sizing for a large mail installation?

Mark Blackman mark at exonetric.com
Mon Sep 27 11:52:00 EDT 2004

On 27 Sep 2004, at 16:38, John Madden wrote:

>> I/O, I/O, I/O -- it's off to work we go!!
>> mail systems need primarily disk bandwidth. Get a killer disk array
>> (fibre-channel or SCSI) and that will keep you happy. The Xeon
>> is nice, but it's disk bandwidth you *need*. I can recommend
>> the StorageTek D-series disk systems, but a bit expensive.
> Fibre channel might be a bit out of our budget, but I could probably  
> get
> my hands on a U320 JBOD on a U320/PCI-X RAID controller (RAID-10,  
> probably
> 14 73GB or 146GB disks).  (I'm thinking the solution would probably  
> end up
> being all-Sun or all-Dell, for reasons beyond my control.)  What sort  
> of
> sustained I/O would you expect to see in this environment?  I expect I
> could easily push a continuous 150MB/s through that setup.

You might get 150MB/s sequential, but not random access. Mail systems
are effectively big database systems and you get very little benefit
from read-ahead caches because you get hundreds/thousands of widely  
disk r/w requests from all over the disk. We used to run a 30K mailbox  
(reasonably busy) and got about 3-4Mbytes/sec of widely scattered  
so I'd look for about 10Mbytes/sec of widely scattered throughput and  
14 disks
will probably handle it ok but make sure it's straightforward to get  
disk array in there if necessary. 10Mbytes/sec is probably overkill but  
definitely be sufficient.

Ideally, you'd want as many spindles as you can afford (14 is a good  
start, although
you may want to consider two 14-disk arrays).

You can either spread your mailboxes across multiple disks and get  
cyrus to worry
about getting the right filesystem for each mailbox (designed for this  
in fact) or
just RAID up the whole array and use it as one big file system.

Mark Blackman

> John
> --  
> John Madden
> UNIX Systems Engineer
> Ivy Tech State College
> jmadden at ivytech.edu
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