[wplug] Thoughts & Considerations for email server

[Bryan J. Smith]

On Sat, 2007-08-18 at 14:48 -0400, Kevin Squire wrote:
> Server is a HP ProLiant ML310 G4 with 
>   - Dual-Core 3050 2.13 GHz
>   - 4GB ram
>   - 4 HDs in a RAID 5 array - totaling ~700GB storage

What are you using for the RAID-5?
Please tell me it's not the FRAID-5 of the ICH?
Or Linux software RAID-5?

First off, I mirror everyone's statements that RAID-5 is _deadly_ for
mail spooling.  Your /var/spool/mail (like anything under /var) should
be on a RAID-10 (or at least RAID-1) volume.  RAID-5 is great for lots
of little reads (and it acts almost like RAID-0 in that regard), but
lots of little writes kill it (like most anything under /var).  99% of
the benchmarks you see on RAID-5 are reads, _ignore_ their marketing.

Secondly, if you're going to be saving $70,000, then _now_ is the time
to strike management.  I would recommend putting forth a sub-$3,000
budget item (which I assume is non-capital) as follows  ...

  1)  Two (2) servers, even if the other is just a spare/standby
      (but mail is easy to load-balance too)

  2)  Increase in disk storage
      (750GB is now commodity)

  3)  Hot-swap bays, including a hardware RAID controller
      (now RAID-5 or RAID-6 becomes an option)

Regarding #1, it's up to you, but you could partition the workload
between servers (for POP/IMAP), as well as have one server as a SMTP
fail-over for the other.  Or I would at least recommend getting a 2nd
server as failover for when the first is down, especially if you don't
have a 4 hour SLA with HP.  ;)

Regarding #2, 750GB is now commodity, with the Seagate Barracuda ES
(24x7 rated version of the Barracuda 7200.10) and Western Digital Caviar
RE (24x7 rated version of the Caviar SE) being two, solid offerings.
RAID-10 would give you 1.5TB, RAID-5 would give you 2.25TB.

Regarding #3, get a 5x3.5" (in 3x5.25") hot-swap enclosure for another
$125 -- 4 bays for production hard drives, and 1 bay to hold a spare
drive.  Yes, get 5 drives, even though one is unused -- you'll thank me
for this when one fails.

And because you can_not_ "guarantee" hot-swap with the Linux kernel (or
any OS for that matter) right now (only select, proven SCSI -- not with
any ATA with a SCSI driver, and _not_ with software RAID, I know people
will argue with me on this, but trust me, I've dealt with _thousands_ of
these "cases" ;), you should have true hardware RAID controller.  A true
hardware RAID controller has on-board intelligence the kernel driver
talks to, and _removes_ the direct access to the drives, so the "volume"
is only presented, so hot-swap is "fool proof."  I recommend 3Ware/AMCC
products.  Looks like you have an older HP DL/ML series (G4) with PCI-X,
so consider a 3Ware/AMCC PCI-X product, like the 9550.

Just some considerations, at least #1 and #2 and, optionally, #3 on the
hardware-side.

Would also mirror some of the MySQL v. PostgreSQL comments, but if
you're already using MySQL, but going to two (2) servers, you could
distribute some of that load.



-- 
Bryan J. Smith         Professional, Technical Annoyance
mailto:b.j.smith at ieee.org   http://thebs413.blogspot.com
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