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Re: RAID card recommendation

From: "Ing(dot) Marcos Ortiz Valmaseda" <mlortiz(at)uci(dot)cu>
To: "Gurgel, Flavio" <flavio(at)4linux(dot)com(dot)br>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: RAID card recommendation
Date: 2009-11-24 20:37:38
Message-ID: 4B0C4412.5060506@uci.cu (view raw or flat)
Thread:
Lists: pgsql-performance
Gurgel, Flavio escribió:
> ----- "Richard Neill" <rn214(at)cam(dot)ac(dot)uk> escreveu:
>
>   
>> Matthew Wakeling wrote:
>>     
>>> We're about to purchase a new server to store some of our old
>>>       
>> databases, 
>>     
>>> and I was wondering if someone could advise me on a RAID card. We
>>>       
>> want 
>>     
>>> to make a 6-drive SATA RAID array out of 2TB drives, and it will be
>>>       
>> RAID 
>>     
>>> 5 or 6 because there will be zero write traffic. The priority is 
>>> stuffing as much storage into a small 2U rack as possible, with 
>>> performance less important. We will be running Debian Linux.
>>>
>>> People have mentioned Areca as making good RAID controllers. We're 
>>> looking at the "Areca ARC-1220 PCI-Express x8 SATA II" as a
>>>       
>> possibility. 
>>     
>>> Does anyone have an opinion on whether it is a turkey or a star?
>>>
>>> Another possibility is a 3-ware card of some description.
>>>
>>>       
>> Do you actually need a RAID card at all? It's just another point of 
>> failure: the Linux software raid (mdadm) is pretty good.
>>
>> Also, be very wary of RAID5 for an array that size. It is highly 
>> probable that, if one disk has failed, then during the recovery
>> process, 
>> you may lose a second disk. The unrecoverable error rate on standard 
>> disks is about 1 in 10^14 bits; your disk array is 10^11 bits in
>> size...
>>
>> We got bitten by this....
>>
>> Richard
>>     
>
> Linux kernel software RAID is fully supported in Debian Lenny, is quite cheap to implement and powerful.
> I would avoid SATA disks but it's just me. SAS controllers and disks are expensive but worth every penny spent on them.
>
> Prefer RAID 1+0 over RAID 5 not only because of the risk of failure of a second disk, but I have 3 cases of performance issues caused by RAID 5.
> It's said that performance is not the problem but think twice because a good application tends to scale fast to several users.
> Of course, keep a good continuous backup strategy of your databases and don't trust just the mirroring of disks in a RAID fashion.
>
> Flavio Henrique A. Gurgel
> Consultor -- 4Linux
> tel. 55-11-2125.4765
> fax. 55-11-2125.4777
> www.4linux.com.br
>
>
>   
Do you expose that performance issued caused by RAID 5? Because this is 
one of our solutions here on my country to save the data of our 
PostgreSQL database. Which model do you recommend ? RAID 0,RAID 1, RAID 
5 or RAID 10?

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Subject: Re: RAID card recommendation
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