[lvm] multi-LUNs storage for mbox : one or many FS?

[Nicoas C.]

Hello,

We are re-thinking the storage of our dovecot mailserver (mbox format). 
We decided to create one LUN on each of our RAID (we have 5 x RAID-5 on 
a SAN), from there we see two possibilities :

  1) creating 5 x VG/LV and filesystems, one for each LUN

   * advantages : we insure that every files stored on the FS remains on 
the same RAID (disks), we can also control the "distribution" of the 
mailboxes on every RAID, if a RAID becomes very solicited, we can move 
the data elsewhere.

   * drawback : we have to monitor and expand 5 independents filesystems 
(we can expect a large number of LUNs after a few expands)


  2) creating a single-big VG/LV/FS spread on all LUNs

   * advantages : we optimize disk occupation with one filesystem and it 
will be very easy to expand and monitor

   * drawback (?) : a mailbox can theoretically have its data present on 
every RAID, I'm not sure if it's a good or a bad thing, mbox files are 
big compared to Maildir but we rarely need to read them entirely

   * drawback : a very bad failure (multiple disks crashing) can 
compromise the entire storage. Also, we have no control on where the 
data are, in case of bad performances, it will be difficult to place 
data "elsewhere" as far as we only have a single FS.

It's a bit OT question because it's not specific to Red Hat, but I think 
this is a good place to ask.

Regards,

Nicolas