Optimal NetRaid Setup

[Vivek Desai]

Hello,

I have 5 (9 gig) drives set up on my Netserver LH3. These are set as Raid 5 on the NetRaid. These physical drives are installed on the Primary Hot-Swap Mass Storage Cage. These drives are all set on Channel 0.

I am planning to add 1 more 9 gig drive on the Primary Hot-Swap Mass Storage cage in the Raid 5 format.

Also I am planning to insert a Secondary Hot-Swap Mass Storage Cage. In this Secondary Hot Swap Mass Storage I am planning to add 3 (9 gig physical drives) more drives.

My question is can you please suggest what channels I should put my these 3 new drives. Would putting it on channel 1 be better?

Also what RAID level should I assign to these 3 physical drives. If I assign them a RAID 5 then is it too risky too have 9 physical drives running on RAID 5. My main goal in adding these drives is to expand the capacity to the fullest.

Final question. When the RAID level is set as RAID 5, I will only lose the data on the FT logical disk if 2 drives fail at the same time? Is this correct?

Thank you for your help.

Best Regards

Vivek

[Alicia White]

Which NetRAID (NR) adapter are you using? Are you just using the LH3's integrated NR? Or, are you using a NR 3si (which has 3 channels)?

If you are using the integrated NR, then your only other choice is to put the 2nd drive cage on Channel 1. If you are using a NR 3si, then it really doesn't matter, you could put the 2nd drive cage on either Channel 1 or Channel 2.

You don't have to add the 4 additional drives to the same RAID5 array. You could do it, but it would probably be better to use the 3 drives on the 2nd channel to create a new RAID5 array. This way, you have increased fault tolerance, in other words, you could have as many as 2 drives fail and still not lose data (1 failed HDD in each array).

Yes, you will lose data if 2 drives fail in the same array.

Alicia

[Vivek Desai]

Hi Alicia,

You are right..I am using the Integrated NetRaid adapter. So the only choice I have is to either put the new drives on Channel 0 or Channel 1.

So if I create a new logical RAID5 array with the 3 new drives I set up on channel 0, will it be possible for me to see all the space(of all the drives installed) as 1 big drive in NT, or will it be divided up in to 2 NT 4.0, since I will have to RAID 5's set up.

Thanks for your help

Vivek

[Alicia White · Accepted solution]

If you create a new RAID5 array using 3 9GB HDDs, once you initialize that new array, NT will "see" that RAID array as a new, unformatted physical drive. Then, you can use NT's disk administrator tool to format and partition the drive anyway you want.

For RAID5 arrays, no matter how many drives are in the array, the space equivalent to one HDD is set aside for the "parity" information. So, in your case, the total space for your new array would be (3 x 9) - 9 = 18GB.

For the RAID5 array on Channel 0, you currently have 5 9GB drives, right? So, the total capacity of the RAID5 array is:
(5 x 9) - 9 = 36GB

If you add a 6th drive, the capacity would increase by 9GB, naturally, and that new space would be seen by NT as if some free space had been added to your existing volume. The total space available would be:
(6 x 9) - 9 = 45GB

Windows NT may or may not allow you to add the new capacity of the 6th HDD on channel 0 or the new array on Channel 1 to your existing logical drive in order to create one huge volume.

Alicia

[Mark Young_2]

Hi Vivek,

Just in support of Alicia's informed Post, I would continue on to suggest that you don't want to put all the drives into one large RAID 5. The main reason is that with each drive you add, the risk of something going wrong increases exponentialy.

A simple example: In a 3 disk RAID 5, if you lose 2 disks, you've lost your data. In a 9 disk array, if you lose only 2 out of the 9 disks, you still lose all your data.

Obviously, you can sometimesget your array back up with multiple drive failures, but I just wouldn't want to risk that much data.

Mark