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Re: Anyone using a SAN?

From: Arjen van der Meijden <acmmailing(at)tweakers(dot)net>
To: Tobias Brox <tobias(at)nordicbet(dot)com>
Cc: Peter Koczan <pjkoczan(at)gmail(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Anyone using a SAN?
Date: 2008-02-13 22:20:57
Message-ID: 47B36D49.10105@tweakers.net (view raw or flat)
Thread:
Lists: pgsql-performance
On 13-2-2008 22:06 Tobias Brox wrote:
> What I'm told is that the state-of-the-art SAN allows for
> an "insane amount" of hard disks to be installed, much more than what
> would fit into any decent database server.  We've ended up buying a SAN,
> the physical installation was done last week, and I will be able to tell
> in some months if it was a good idea after all, or not.

Your SAN-pusher should have a look at the HP-submissions for TPC-C... 
The recent Xeon systems are all without SAN's and still able to connect 
hundreds of SAS-disks.

This one has 2+28+600 hard drives connected to it:
http://tpc.org/results/individual_results/HP/hp_ml370g5_2p_X5460_tpcc_080107_es.pdf

Long story short, using SAS you can theoretically connect up to 64k 
disks to a single system. And with the HP-example they connected 26 
external enclosures (MSA70) to 8 internal with external SAS-ports. I.e. 
they ended up with 28+600 harddrives spread out over 16 external 4-port 
SAS-connectors with a bandwidth of 12Gbit per connector...

Obviously its a bit difficult to share those 628 harddrives amongst 
several systems, but the argument your colleagues have for SAN isn't a 
very good one. All major hardware vendors nowadays have external 
SAS-enclosures which can hold 12-25 external harddrives (and can often 
be stacked to two or three enclosures) and can be connected to normal 
internal PCI-e SAS-raid-cards. Those controllers have commonly two 
external ports and can be used with other controllers in the system to 
combine all those connected enclosures to one or more virtual images, or 
you could have your software LVM/raid on top of those controllers.

Anyway, the common physical limit of 6-16 disks in a single 
server-enclosure isn't very relevant anymore in an argument against SAN.

Best regards,

Arjen

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