Date: Thu, 29 Sep 2005 17:25:49 +0300
From: Michael Ben-Nes <miki@canaan.co.il>
Subject: Re: Advice on RAID card
In-reply-to: 
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To: Ron Peacetree <rjpeace@earthlink.net>
Cc: PFC <lists@boutiquenumerique.com>,
	pgsql-performance@postgresql.org
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I think the answer is simple


if the question is low end Raid card or software ? go on the software 
and youll get better performance.

If this is a high end server i wouldnt think twice. HW RAID is a must 
and not only because the performance but because the easynes ( hot swap 
and such ) and the battery


Ron Peacetree wrote:

>While I understand being economical, at some point one crosses the line
>to being penny wise and pound foolish.
>
>How much is the data on this server going to be worth?
>How much much will it cost you to recover or restore it (assuming that
>is even possible if you lose it)?
>
>If your data is worth nothing or the cost to recover or restore it is
>negligible, then you don't need (nor should want) a DB server.  You'll
>get higher performance at less cost via a number of other methods.
>
>OTOH, if you data _does_ have value by any of the above metrics,
>then it is worth it to pay attention to reliable, safe, fast, physical IO.
>
>Battery backed HD caches of appropriate size are usually well worth
>the $, as they pay for themselves (and then some) with the first data
>loss they prevent.
>
>RAID 5 means you are _always_ only 2 HDs from data loss, and 1 HD
>from a serious performance hit.  Part of the trade-off with using SATA
>HDs that cost 1/3-1/4 their U320 15Krpm brethren is that such
>circumstances are +FAR+ more likely with SATA HDs.  
>
>If you are not going to use RAID 10 because of cost issues, then
>spend the $ to get the biggest battery backed cache you can afford
>and justify as being cheaper than what the proper RAID 6 or RAID 10
>setup would cost you.  Even if you are going to use SW RAID and the
>controller will just be a JBOD controller.
>
>On the general subject of costs...  
>
>At this writing, SODIMM RAM costs ~$100 (US) per GB.  Standard
>DIMMs cost ~$75 per GB unless you buy 4GB ones, in which case
>they cost ~$100 per GB.
>
>The "sweet spot" in SATA HD pricing is ~$160 for 320GB at 7200rpm
>(don't buy the 36GB or 74GB WD Raptors, they are no longer worth
>it).  If you are careful you can get SATA HD's with 16MB rather than
>8MB buffers for that price.  Each such HD will give you ~50MB/s of
>raw Average Sustained Transfer Rate.
>
>Decent x86 compatible CPUs are available for ~$200-$400 apiece.
>Rarely will a commodity HW DB server need a more high end CPU.
>
>Some of the above numbers rate to either fall to 1/2 cost or 2x in value
>for the dollar within the next 6-9 months, and all of them will within the
>next 18 months.  And so will RAID controller costs.
>
>Your salary will hopefully not degrade at that rate, and it is unlikely that
>your value for the dollar will increase at that rate.  Nor is it likely that
>data worth putting on a DB server will do so.
>
>Figure out what your required performance and reliability for the next 18
>months is going to be, and buy the stuff from the above list that will
>sustain that.  No matter what.
>
>Anything less rates _highly_ to end up costing you and your organization
>more money within the next 18months than you will "save" in initial
>acquisition cost.
>
>Ron
>
> 
>
>
>
>-----Original Message-----
>From: PFC <lists@boutiquenumerique.com>
>Sent: Sep 24, 2005 12:27 PM
>Subject: Re: [PERFORM] Advice on RAID card
>
>
>  
>
>>It looks like a rebranded low end Adaptec 64MB PCI-X <-> SATA RAID card.
>>Looks like the 64MB buffer is not upgradable.
>>Looks like it's SATA, not SATA II
>>    
>>
>
>	Yeah, that's exactly what it is. I can get one for 150 Euro, the Areca is  
>at least 600. This is for a budget server so while it would be nice to  
>have all the high-tech stuff, it's not the point. My question was raher,  
>is it one of the crap RAID5 cards which are actually SLOWER than plain IDE  
>disks, or is it decent, even though low-end (and cheap), and worth it  
>compared to software RAID5 ?
>
>  
>
>>Assuming you are not building 1U boxes, get one of the full height
>>cards and order it with the maximum size buffer you can afford.
>>The cards take 1 SODIMM, so that will be a max of 1GB or 2GB
>>depending on whether 2GB SODIMMs are available to you yet.
>>    
>>
>
>	It's for a budget dev server which should have RAID5 for reliability, but  
>not necessarily stellar performance (and price). I asked about this card  
>because I can get one at a good price.
>
>	Thanks for taking the time to answer.
>
>
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>

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