RAID config for mailboxes host

Hello,

Slightly OT because not Debian specific.

Let this physical server:

    Dell R710
    2x6 cores 2.3 GHz
    48 GB RAM
    12 disks 600 GB, 15 ktr/min
    only one RAID card H700

for the usage of a rather small mailhost:

    MDA
    IMAP/POP for 1500 mailboxes (Maildir)
    webmail
    (MX are other machines)

We consider two RAID config for the 12 disks:

        A   2 disks RAID 1 for system
           10 disks RAID 6 for mailbox space

        B  12 disks RAID 6 for the whole 

In A, we lose 1.2 (raw) TB with respect to B. Advocates of A say that
in B, the heads read/write activity of the mailboxes will seriously
impact the system performance. In A, the system has its own axes,
separate from the mailboxes ones.

Side note: We are considering dovecot.

Do you think that the performance loss will be so visible that it
worth sacrifying 1.2 TB of mailbox space?

Facts are far better than guesses, but how to bench those two configs,
with which test protocol, and how realistic?

Thanks,

-- 
Emmanuel Halbwachs                       Observatoire de Paris-Meudon
Resp. Réseau/Sécurité                           5 Place Jules Janssen
tel  :  +33 1 45 07 75 54                        F 92195 MEUDON CEDEX
fax  :  +33 1 45 07 01 89      véhicules : 11 av. Marcellin Berthelot


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