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Old 01-20-2005, 01:49 PM   #1
hamish
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hardware/software raid: clarification


Hello

I recently acquired a server which has onboard FastTrak 100 ATA Raid controller. I would like to RAID 1 the two 20gb drives in the server.

From my understanding of RAID 1, when something is written to hard drive 0, it is automatically written to hard dtive 1 as well. Is this correct?

My second question is, which part of the computer does this part of the RAID action (that is, mirrorring)? I was under the impression that hard ware RAID did that is well as software raid (possible better in some cases). I thought that having a raid controller (into whose bios I can enter and set up/delete/repair arrays) would do the mirroring.

HOwever, after some testing, it seems that it doesn't automatically mirror everything. I think found reference to some software for this controller. It seems that there is also a software part of this bundle. Is this possible? Do hardware raid devices only set up the array, and then a software device (like Linux softraid modules) is responsible for the mirroring?

Could someone please help me clarify.

Thanks in advance.
Hamish
 
Old 01-20-2005, 05:33 PM   #2
david_ross
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Re: hardware/software raid: clarification

Quote:
Originally posted by hamish
From my understanding of RAID 1, when something is written to hard drive 0, it is automatically written to hard dtive 1 as well. Is this correct?
That's right.

Quote:
Originally posted by hamish
My second question is, which part of the computer does this part of the RAID action (that is, mirrorring)? I was under the impression that hard ware RAID did that is well as software raid (possible better in some cases). I thought that having a raid controller (into whose bios I can enter and set up/delete/repair arrays) would do the mirroring.
The hardware should do this and you can configure the arrays by pressing ctrl+F to get into the fasttrak bios during boot.

Quote:
Originally posted by hamish
HOwever, after some testing, it seems that it doesn't automatically mirror everything. I think found reference to some software for this controller. It seems that there is also a software part of this bundle. Is this possible? Do hardware raid devices only set up the array, and then a software device (like Linux softraid modules) is responsible for the mirroring?
In theory hardware raid should be transparent but these FastTrak controllers in particular are very software dependant. You will really never get away from having some software as you really need something to monitor the state of the array. finegan swears by 3ware if you want the best, I haven't tried it myself but he's the man to listen too:
http://www.linuxquestions.org/hcl/showcat.php?cat=273

With most proccessors now being more than adequate, software mirroring at RAID 1 isn't a bad option at all since it is really just writing to two disks and there is no striping involved. I'm hoping to do this in my own server with 2 nice new SATA drives myself soon.
 
Old 01-20-2005, 05:48 PM   #3
hamish
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hey
I have a P3 1ghz with a gig of ECC ram. That is sufficient to do software raid 1, do you think?

Thanks for all your help. The problem I'm now come against is that my server doesn't boot because the /boot partition is /dev/hde (because the fast trak has its own controllers) That is, I have 4 IDE adapters on my mobo. The BIOS only has the option to boot from the first two, so my hard drive, which is on the 3rd adapter, isn't recognied. I'll work on this, although, it seems that maybe software RAID is what I'm after.

There is more flexibility with software RAID, isn't there? That is, if my server was in colocation and a the array broke with hardware RAID, I would need to go down and reboot it to fix the array from the RAID BIOS, yet? But with linux soft raid, I could do it with SSH.

thanks
Hamish

Last edited by hamish; 01-20-2005 at 05:52 PM.
 
Old 01-22-2005, 12:39 PM   #4
david_ross
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Quote:
Originally posted by hamish
hey
I have a P3 1ghz with a gig of ECC ram. That is sufficient to do software raid 1, do you think?
I would say so. Generally anything of that spec should be fine for most purposes the the probable exception of a busy fileserver.

Quote:
Originally posted by hamish
Thanks for all your help. The problem I'm now come against is that my server doesn't boot because the /boot partition is /dev/hde (because the fast trak has its own controllers) That is, I have 4 IDE adapters on my mobo. The BIOS only has the option to boot from the first two, so my hard drive, which is on the 3rd adapter, isn't recognied. I'll work on this, although, it seems that maybe software RAID is what I'm after.
The chances are that you haven't installed the fasttrak drivers right, it took me a long time to get to grips with it. If you boot the system without the software part of the driver you just get 2 ide drives showing up. With the fast trak driver loaded these become a virtual drive such as /dev/sda as opposed to /dev/hde and /dev/hdg.

Quote:
Originally posted by hamish
There is more flexibility with software RAID, isn't there? That is, if my server was in colocation and a the array broke with hardware RAID, I would need to go down and reboot it to fix the array from the RAID BIOS, yet? But with linux soft raid, I could do it with SSH.
Yes and no. You are right that is generally easier to control the raid but most raid failures are due to hardware failures so a drive is still likely to need replacing.

The best guide to software raid on linux is:
http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html
 
Old 01-24-2005, 03:23 AM   #5
Emmanuel_uk
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hard/soft clarification in raid0 Sil3112A

Hi,

I understand the SiL3112A is a software raid really.
But what is the use of the bios option for the SiL3112A to offer
a choice of chunk sizes for the raid0 mode, when
the chunk size can be superseeded by mdadm?
Does the bios option matters at all under linux (for this hardware)?
Which chunk size is actually used by the hard drive then?

Thank to anybody who could clarify the hardware vs. software issue.

Thanks
Regards

PS: I followed partly the software raid howto from tldp.org
and have a raid0 working ok (managed by mdadm)

Last edited by Emmanuel_uk; 10-12-2006 at 01:55 AM.
 
  


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