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-   -   Fake raids are becoming common, so I ask you how should it be set up? (http://www.linuxquestions.org/questions/linux-hardware-18/fake-raids-are-becoming-common-so-i-ask-you-how-should-it-be-set-up-836860/)

darkstarbyte 10-07-2010 09:58 PM

Fake raids are becoming common, so I ask you how should it be set up?
 
Fake raid hard drives are becoming more common and I am wondering how to set them up. This is what I have been told, and you are welcome to disagree (as long as we can agree to disagree).

From what I have seen and heard it appears to me that to set up a fake raid in Linux you partition the separate volumes and format them, but when you install your operating system you have to go into fstab and merge the separate volumes into the root partition.

mostlyharmless 10-08-2010 03:25 PM

Umm, no. Many distros automagically handle fakeraid using dmraid, and I believe mdadm >3.0 handles some of these as well. There are any number of howtos floating around depending on your distro.

carlosinfl 10-08-2010 07:21 PM

I don't know if there's a right or wrong way to configure 'fake RAID' on a specific server so here's my home server:

Code:

Personalities : [raid1]
md2 : active raid1 sda3[0] sdb3[1]
      731977536 blocks [2/2] [UU]

md1 : active raid1 sda2[0] sdb2[1]
      96320 blocks [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
      497856 blocks [2/2] [UU]

unused devices: <none>

Filesystem            Size  Used Avail Use% Mounted on
/dev/md2              688G  2.6G  650G  1% /
/dev/md1              92M  16M  72M  18% /boot


jefro 10-08-2010 10:16 PM

It don't trust them, I have seen too many gimpy raid cards act weird. Get a real hardware raid or don't use them at all.

darkstarbyte 10-09-2010 05:27 PM

A hard ware raid is faster than a software raid, but a software raid in theory is more reliable.

lpallard 10-10-2010 10:39 AM

Here's my :twocents: on the subject...

Fakeraid (mobo's so-called raid controllers as well as 99% of those cheap raid add-on cards) are not so reliable, I had 3 bad experiences in the last 10 years with these, with fried controllers and one of them that became nuts and corrupted the whole array... I will never buy again one of these add-on cards (either PCI or PCI-e) for their RAID capabilities. A real RAID (hardware) controller costs lots of $ but is more reliable. There is a reason why some goes for $39 while others go for $799...

Like I just said, if you want hardware controlled RAID, I would uggest going with real controllers, but be ready to spend lots of money. I really don't think for home usage it is worth it.

The problem with hardware (either fakeraid or real raid) is that you add hardware components to the whole system... By adding such extra hardware layer, you increase the probability of failure and decrease the reliability of the system. That's why I said for hardware controlled RAID, I would go with commercial class because these components have a better documented reliability and apparently their quality control (I did not confirm this) is supposed to be better.

I personally use software RAID (using mdadm). I recently lost a almost brand new WD caviar green and most of the data that was on it. My mobo has a fakeraid controller, but like I always do, I enter the bios and setup the controller as standard SATA controller or depending on your BIOS, deactivate it. Then I setup a software raid 1 array with 2 hard drives. My whole system runs on RAID1 while other partitions are only backed up using rsnapshot.

As far as I know, the main differences are speed, performance and reliability. Hardware raid (real one) might be better in the two first, but I believe software RAID is more reliable. Again I should mention instantaneous reliability VS long term reliability...

With fakeraid, I believe you dont have the performance of real raid while you have lower reliability. You get the worst of both worlds.

I might be wrong but this is my experience... I hope it helped.


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