RAID: Permutation & combinations???

[tarun_34]

Hello friends,
this is my first post on this forum so please enlighten me on this issue even if it sounds silly..... :roll:

I've read so much about raid (0, 1 0+1) these days but never come across any article which has mentioned setting up a RAID of more than two disks....my questions are : -

1) A motherboard which might have three raid controllers, in reality how many disks are possible to be set up in raid configuration because all i've read is that a single controller supports a maximum of 4 disks, so lets say if i want to get a six disk RAiD setup, is it possible to simultaneously use 2 raid controllers- one with 4 disk and another with 2 disk. Or we can only use one raid controller at a time from a motherboard having 3 controllers???? If this is the case then why do some mobo boast of 8 sata connectors???

2) Is it possible to use 2 disks (out of 4 HDDs) as a RAID 0 or 1, and the other two HDDs as non-RAIDs, in the same raid controller??

3) Does having a RAID 0 setup effect the life of hard drives??? Are HDD more prone to failure in RAID 0 setup or the chances would be the same as any normal non-RAID drive??

4) Will having a 4 disk raid setup improve performance substantially or will be it meagre compared to 2 disk setup.Which would be better :-
(A) 2 western digital raptor, 75 GB, 10000 RPM
OR
(B) 4 (disk) 160 GB 7200 RPM sata drives in terms of performance (in RAID 0 setup)?

5) Finally, what are disk failure rates, coz personally have never seen a disk fail till date. Is it really something that should make us go for a RAID 1 setup????

Well these are a volley of questions, but would really appreciate if you could share your knowledge on all/any of these points......Thanx in advance dudes!!!!

 

[pradeep_chauhan]

Oh A long list so here goes.
The number of disk supported depend upon the controller say a silicon image 3112 supports 2 disks and can have raid 0, 1 (or 1+0) Similarly a si 3114 will use 4 disks to give raid 0,1,5 .... These are examples of sata /ide disks in scsi one controller can support a max of 15 disks with any raid level. Also the big big Q to see is the raid type all the current mobo give you a software raid solution this is not very efficent and has a higher cpu utilisation a hardware raid sol is very expensive as it requires the raid card to have irs own cpu and memory there are the actual raid controllers and give good results.
Setting up raid across controllers is not possible (as far as i know) The disk across raid controllers can be used as a single disk called JBOD. The mobo with multiple raid controllers have these so as to set up volumes of raids each raid will finaly give them one disk (with partitions) so to have multiple disks multiple controllers are used. A pice of advice do not bank for the mobo based raid solutions they are a pain with no performance.

2) Is it possible to use 2 disks (out of 4 HDDs) as a RAID 0 or 1, and the other two HDDs as non-RAIDs, in the same raid controller??

Yes its possible to use part of disks / different disks in diffrent manner.

3) Does having a RAID 0 setup effect the life of hard drives??? Are HDD more prone to failure in RAID 0 setup or the chances would be the same as any normal non-RAID drive??

No nothing like this is docummented but disks used in raid 0 do have a lesser oad than a normal disk so simple logic says they should last longer. See the killer for disks is the cycle time eg a scsi disk has a MTBF (running) of 12,00,000 hrs where a cycle life of just 25000 data seagate) so the on/off is what kills a disk not usage.

4) Will having a 4 disk raid setup improve performance substantially or will be it meagre compared to 2 disk setup.Which would be better :-
(A) 2 western digital raptor, 75 GB, 10000 RPM
OR
(B) 4 (disk) 160 GB 7200 RPM sata drives in terms of performance (in RAID 0 setup)?

Yes a 4 disk raid 0 is much better than a 2 disk raid there are four channels of data in/out. I personaly think 2 western digital raptor, 75 GB, 10000 RPM is the option i will go for.

5) Finally, what are disk failure rates, coz personally have never seen a disk fail till date. Is it really something that should make us go for a RAID 1 setup????

it depends how important your data is if its mission critical use raid 1 or better solutions HARD DISKS DO FAIL (That too at the most wanting times ... Remember Murfies (sp ?) Laws).

 

[Astrix]

No nothing like this is docummented but disks used in raid 0 do have a lesser oad than a normal disk so simple logic says they should last longer. See the killer for disks is the cycle time eg a scsi disk has a MTBF (running) of 12,00,000 hrs where a cycle life of just 25000 data seagate) so the on/off is what kills a disk not usage.

Thanks, pradeep! That makes me comfortable about going in for RAID.

So basically if I have two 80gb's in raid0 I can use them like a 160gb drive?

 

[pradeep_chauhan]

please dont wait listen to my sob story. Itoo wanted to setup raid 0 using seagate sata 160 GB so went bought the disk and the silicon immage 3112a card pluged in every thing then found out that the card supports only software raid that too in windows xp.( I use Gentoo) so ran back to return the stuff but had no luck in returning the disk (reason:i had opened the plastic wrapper) so stuck with a 160GB disk and no raid.

 

[KHUBBU]

And we have some people saying that new members shud be allowed to post a new topic only after 10 posts.

Good question tarun. I too wanted to know about it.
Can anyone give links to some tutorial on how to setup raid and related links.
Thanks

 

[pradeep_chauhan]

I personaly feel the quality of the question asked by any one be it a vetron or a green horn is a clear indicator of
a. How genuine is the problem
b. Has he worked on it.
c. What does he want
i. Increase his post count
ii. cause a heated exchange and lie back and enjoy the show
iii Bost of xxx replies to his question.
iv Solution to the problem
d. Show off his knowledge (he knowes the answer before hand and is just testing others)
I do not want to offend any one its just a simple observation i have being here for the past six monts or so.

 

[tarun_34]

thanx!!!!

Thanx pradeep.......that was one thorough explanation and definitely the one i was looking for!!! .......thanx dude not just for clearing all my doubts (lots of them) but also for posting a quick response.....you guys rock!!! 8)