[nflug] RAID

Corey Reichle coreyreichle at verizon.net
Mon Feb 11 09:49:25 EST 2008 

Build the RAID0 devices, then use assemble those into a RAID1.

Use fdisk to create partions on the disks, of type "Linux RAID"

mdadm --create /dev/md0 --level=0 /dev/{fill in the components}
mdadm --create /dev/md1 --level=0 /dev/{fill in the components}
mdadm --create /dev/md2 --level=1 /dev/md{0,1}

Afterwards, use mdadm -A to assemble the arrays after reboot.  I don't know how to make them auto assemble yet, I think RHEL5 does it, but not sure.  Ubuntu does, just haven't read into it too much.  I generally use hardware RAID...

Read through the man page for mdadm.  There are a lot of tuning options, such as chunk size, # of devices, # of spares, et al.
=====================
From: Eric #4011 <eric at bootz.us>
Date: 2008/02/11 Mon AM 08:14:39 CST
To: nflug at nflug.org
Subject: Re: [nflug] RAID

I really like the RAID 0+1 idea but I'm not sure how to do it with Linux 
software RAID, do I need to create two RAID 0's and then combine them 
with a nested RAID 1 to achieve RAID 0+1.  I will consider RAID 5 as 
suggested.


Corey Reichle wrote:
> You need to consider this:  RAID0 is the best performance wise, but at the risk of a single drive going will bring down the array.
>
> RAID1 will get you some fault tolerance, but it takes a hit since two physical writes for every logical write.  The only way to circumvent much of the performance loss is separate controllers.
>
> I would suggest RAID5.  Best performance gain for fault tolerance, as well as increased performance over a RAID0 with the right controllers.
>
> ====================
> From: Eric #4011 <eric at bootz.us>
> Date: 2008/02/11 Mon AM 07:01:46 CST
> To: nflug at nflug.org
> Subject: Re: [nflug] RAID
>
> Great, I'll use Raid Software then.
>
> Space isn't a problem each drive is 160GB and it's just a small email 
> server of about 100 people, so raid 0 or 1 would be best for performance?
> these are also hot swap drives does a certain raid matter in this instance?
>
> Thank you,
> Eric
>
> Mark Musone wrote:
>   
>> I'd probably use software raid over most onboard SATA raid controllers..
>>
>> You may also want to consider raid-5, since you'll get more usable storage
>> space than raid0-1
>>
>> Mark
>>
>>
>> -----Original Message-----
>> From: nflug-bounces at nflug.org [mailto:nflug-bounces at nflug.org] On Behalf Of
>> Eric #4011
>> Sent: Friday, February 08, 2008 3:36 PM
>> To: nflug at nflug.org
>> Subject: Re: [nflug] RAID
>>
>> Yes it does help, and I want to be sure I do this the right way.  The 
>> board is a TYAN Tomcat K8E using a Nvidia RAID controller for SATA 
>> drives... I have heard that the onboard RAID controllers are not that 
>> great, however which is better poison the Linux RAID software or the 
>> onboard RAID controller?
>>
>> Rob Dege wrote:
>>   
>>     
>>> It's been a while since I've spoken in RAID, but I think your 
>>> terminology is off.  RAID-0 by default requires at least two hard 
>>> drives in order to configure.  The same goes for RAID 1.
>>>
>>> So, in this instance, you will use two drives to create a RAID-0 
>>> array.  This array now appears as a single drive.  You then create 
>>> another RAID-0 array using the other two disks.  This array now 
>>> appears as a single drive.  So now, you have two RAID0 arrays 
>>> independent of each other.  Finally, you create a RAID-1 mirroring 
>>> array, using the two RAID-0 disks that you just created.
>>>
>>> Thus, you now have a single drive, with the capacity of two drives.  
>>> If this is all handled within the RAID controller, linux will only 
>>> acknowledge the existence of this RAID-0+1 drive as a single disk.  So 
>>> you won't be able to use the linux software RAID to create another 
>>> layer of mirroring.
>>>
>>> Of course, this is assuming that your RAID controller is doing all of 
>>> the array structure and work.  Most of the onboard RAID controllers in 
>>> today's motherboards, and built shoddy.  Their contain the cheap 
>>> hardware, but you need to install software to configure/access the 
>>> onboard controller.
>>>
>>> Plus, it's been a while, but I do recall some warning about not 
>>> putting either the root directory or the /boot directory on a raid.  
>>> It has something to do about the module needed by the kernel to 
>>> identify the raid drive being stored on the raid drive or something 
>>> like that.
>>>
>>> oh well, hope this helps somewhat.
>>>
>>> -Rob
>>>
>>>
>>> On Feb 8, 2008 12:49 PM, Eric #4011 <eric at bootz.us 
>>> <mailto:eric at bootz.us>> wrote:
>>>
>>>     Hi, I was wondering if the following RAID configuration is possible?
>>>
>>>
>>>     I have 4 SATA drives for RAID and am using MediaShield utility to
>>>     configure a RAID 0+1
>>>
>>>     
>>>       
>> ****************************************************************************
>> *******************
>>   
>>     
>>>     MediaShield States RAID 0+1 is:
>>>             RAID 0 drives can be mirrored using RAID 1 techniques,
>>>     resulting in a RAID 0+1 solution
>>>             for improved performance plus resiliency
>>>             The controller combines the performance of data striping (RAID
>>>     0) and the fault tolerance
>>>             of disk mirroring (RAID 1). Data is striped across multiple
>>>     drives and duplicated on
>>>             another set of drives.
>>>
>>>     
>>>       
>> ****************************************************************************
>> *******************
>>   
>>     
>>>     After this I have two drives and I am ready to install
>>>     linux(debian etch)
>>>
>>>     My thoughts are if I also use RAID 1 software(linux) with the existing
>>>     two drives I will have one hard drive writing to three hard drives?
>>>
>>>     I'm wondering if this is possible?
>>>
>>>     Thank you in advance for your explanations
>>>
>>>     Thank you,
>>>     Eric
>>>     _______________________________________________
>>>     nflug mailing list
>>>     nflug at nflug.org <mailto:nflug at nflug.org>
>>>     http://www.nflug.org/mailman/listinfo/nflug
>>>
>>>
>>>
>>>
>>> -- 
>>> -Rob
>>>
>>> Ben Franklin Quote: "They that can give up essential liberty to obtain 
>>> a little temporary safety deserve neither liberty nor safety."
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
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>>>   
>>>     
>>>       
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