[mdlug] New Server - Hardware Configuration

[Aaron Kulkis]

Michael ORourke wrote:
> 
> ----- Original Message ----- 
> From: "Aaron Kulkis" <akulkis00 at gmail.com>
> To: "MDLUG's Main discussion list" <mdlug at mdlug.org>
> Sent: Wednesday, April 25, 2012 6:58 AM
> Subject: Re: [mdlug] New Server - Hardware Configuration
> 
> 
>> Michael ORourke wrote:
>>> What about a small SAN device?  Also, you could attach an iSCSI SAN to a
>>> front-end Linux server.  Another thing you didn't mention was backups.
>>> Having multiple RAID sets is NOT a backup strategy.  This is a common
>>> mistake many people make.
>>
>> Mirroring over SAN????
>>
>> No... just no.
>>
>> Way too slow.
> 
> That's strange, I don't recall recommending that.
> But I agree that it can be slow.
> 
>>
>>> If it were me, I would try to seperate the storage from the server. 
>>> Perhaps
>>> with a RAID6 configuration and a hot spare.  That way you could lose up 
>>> to 3
>>> drives and still be fully operational.  There are several low cost SAN
>>> vendors out there which are certainly worth a look.  I don't quite
>>> understand why they are pushing a server with 3 RAID cards.  Sounds like
>>> this might become an expensive and difficult to support file server.
>>>
>>
>> A SAN is nothing more than a file server.
> 
> I guess it depends on the SAN device, but yes, it can be a file server.
> 
>> Now you're converting this into a file server with external storage
>> in another file server.  By this logic, we should implement the
>> SAN with a small box and ITS hard drives in a 3rd box...which are
>> actually located in a 4th box... ad infinitum or until the budget
>> runs out.
>>
>> So... maybe the best thing to do is just keep the disk drives
>> in the same box, and keep things as simple as possible.
>>
> 
> Okay, I get  your point.  My thought was, if you are going to roll-your-own 
> server
> with a bank of disk drives and multiple controllers, then why not just throw 
> in a SAN,
> carve up the volumes, and be done with it.
> It seems that managing multiple RAID sets of hot-swapable drives, volumes, 
> and
> disk clone jobs is going to be a big headache.
> 
>> All the SAN does is in this case is introduce additional points
>> of failure without any increase in system reliability or data
>> availability.
> 
> Yes it does introduce additional hardware into the mix.  So that's a valid 
> point, but is
> trying to cram everything into one giant server box really more reliable or 
> provide a
> higher data availability solution?


Well, if you need a lot of space, get a BIG box with redundant power
supplies, and/or you might want to investigate external expansion disk
arrays.  And max out your fan capacity.  Look for cases with one or
more of those nice 12-inch fans on the side -- they can move a lot
of air while still turning slowly (longer bearing life and low noise).

SATA or SAS is a lot faster than any form of Ethernet, and frankly,
a lot less problematic than a SAN or NAS (the only way I would
recommend using SAN or NAS is if you had the budget for something
in the $50,000+ range.  Since I understand that you're pressed to
keep the price down, the sort of NAS or SAN that you can buy just
adds another point of failure without increasing system reliability,
thereby

You have to look at this like a gambler -- if a gambler were
betting on your system staying up or not, he's going to want
you to have as complex a system as possible, and he's also going
to want you to have little to no redundancy.
So, to bet against him, you want a system which is physically
as simple as possible, and has as much redundancy as possible.


Lastly, remember that airflow in and out of the case obeys
Kirchoff's current law.  One the pressure differential in the
case has been established, Airflow(out) = Airflow(in).

If your case were a pizza box, the ideal would be for all
fans blowing in the same direction (in), with ample amounts
of screens for an equal amount of out-flow using no additional
fans.

In real life, however, big servers are not pizza boxes.
We want cool air drawn in at  the bottom (not blown out), and
we want hot air removed from the top (not drawn in), and so
the "ideal" set-up for the pizza box -- all fans blowing in
the same direction with completely free flow through ample
vent-holes will never be realized.

That being said, I would, if you have the time, take a few
hours to improve the case.  Put some filtration material (even
real low-cost 1970's type furnace filter, or even foam filter
material attached over any orifice in which airflow enters
the case is a good thing -- it keeps dust out of your card
slots.  Due to  mechanical vibration, dust will ALWAYS work
its way deeper and deeper into a card slot until eventually,
one of your contacts has a complete electrical disconnection
due to a thin, and not even complete, layer of dust.

Lint and dust are enemies in the perpetual war to keep your
chips and hard drives cool.

It sounds like your project is important, so splurge a few
tens of dollars on keeping the air inside the case clean.
If you feel extra-handy, make an auxillary case that does
nothing but draw air through a nice big furnace filter that
uses pleated filter paper, and make some duct-work (cardboard
and duct-tape will do) leading the air off to your air intakes.
Such a thing doesn't have to be huge -- just a few inches
of air space behind the removable filter.

Static type filters are also acceptable.... they cost about
3x more than a HEPA filter, but they are completely reusable.
Just take a dirty one to the janitor's closet, spray it with
some mild solution, and spray out with a hose, then let it dry.
If you decide to go this route, buy 2.  That way you don't
have to put a just-cleaned, WET filter back into your assembly.

Also, washable static type filters also tend to be made with
a plastic adjustable-size frame -- you can cut the filter to
the EXACT size that you want -- so it's much nicer than the
pleated filters.