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Choosing the right Raid setup

post #1 of 8
Thread Starter 
I got a couple basic questions... having never set up any raid before.

I want to run 6 drives in a 5+0 (I think ) but I want to know if I can do this and have my os boot off of those drives.

Also with a 5+0 setup is there much of a performace increase over simply running dual raid 5 set ups?

Thanks,
Wes
post #2 of 8
I am assuming that you have a controller card that supports RAID5+0 (more commonly known as RAID50)

Effectively, as you know, RAID50 basically is nothing more than two RAID5 arrays that are combined in a RAID0 array. You'll loose the total space of two drives out of the six for the parity in each of the RAID5 arrays.

Speed will indeed be better than two separate RAID5 arrays, but it depends on the controller a bit. You need a high-quality controller, since RAID50 takes a lot of CPU overhead (which will be taken care of by the controller if it's a good enough one )

Why not just one large 6-disk RAID5, or even RAID6 if you need the extra security, array?
    
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post #3 of 8
Thread Starter 
Quote:
Originally Posted by Chozart View Post
I am assuming that you have a controller card that supports RAID5+0 (more commonly known as RAID50)

Effectively, as you know, RAID50 basically is nothing more than two RAID5 arrays that are combined in a RAID0 array. You'll loose the total space of two drives out of the six for the parity in each of the RAID5 arrays.

Speed will indeed be better than two separate RAID5 arrays, but it depends on the controller a bit. You need a high-quality controller, since RAID50 takes a lot of CPU overhead (which will be taken care of by the controller if it's a good enough one )

Why not just one large 6-disk RAID5, or even RAID6 if you need the extra security, array?
I have not yet purchased a controller... until I figure out exactly how I want to set it up.

I read that RAID5 has diminishing returns (in terms of security) the more drives you use. Mainly to me that means I would be better off running 2 RAID5 set ups because with 2 drive failures in 1 RAID5 would make the whole array fail... meaning if I have 2 drive failures with 2 RAID5's running my worst data loss will be half of the total (or possibly none if only 1 drive per array fails) where as one large RAID5 2 dead drives leads to failure of all the data...

I may be wrong... thats how I interpreted what I read.

I don't understand RAID6 quite as well, but I thought it was for larger arrays--and that performance suffered significantly...

We basically have a server in the house that I want to stack with around 4-5tb of space. My main concern is data security... at most we have 4-5 computers using the server at once playing video/etc... so I'm hoping not to sacrifice too much speed.
post #4 of 8
Quote:
Originally Posted by mrwesth View Post
because with 2 drive failures in 1 RAID5 would make the whole array fail
Mrwesth, it also depends on how many drives are in the RAID5 array. If you have 3 drives in RAID5 and 2 fail then yes you'll run into problems but you can have more then 3 drives on a RAID5. Some controllers allow dozens of drives in RAID5. If you want I/O then more drives the better.
If your budget is unlimited(which would be cool) then check out SCSI/SAS or fibre channel. That's where the performance is at.

Good luck
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post #5 of 8
RAID5 is similar to RAID6, but with two parity stripes. I.E., two drives can fail.

Plus, with modern drives, what's the true failure rate? It's pretty darn low.

thlnk3r: LOL... if he wants 4-5TB, with SAS indeed you'll need an unlimited budget I think the largest SAS drive is in the ~300GB range, and hundreds of dollars for a single drive.

Have you thought about RAID10 or RAID0+1? In those cases, you can use the onboard controller (performance will be as good as RAID50 or RAID6 on a dedicated true hardware controller). You'll need eight (8) 1TB drives to get 4TB of storage space. With, for example, these Seagates, that'll cost you $1,679.92

The alternative is RAID50 with six of those drives on a dedicated controller. Six of the same Seagates will ring you up $1,259.94 and a decent controller card that supports RAID50 will cost you $449.99. Total cost: $1,709.93. Basically a tie, but RAID10 or RAID0+1 is much easier to rebuild in case of failure.

Personally, I do NOT recommend RAID for ANY important data... I'd highly consider a SINGLE external drive for your most critical data (or a tape device...). Then schedule nightly backups to that drive. The issue with RAID is that the moment you replace the RAID controller with another type, you'll have to rebuild the RAID array. Imagine that in a year or two your RAID controller bites the dust, and it's impossible to get a replacement. Ok, worst case scenario, but still.
    
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post #6 of 8
Quote:
Originally Posted by Chozart View Post
I'd highly consider a SINGLE external drive for your most critical data (or a tape device...).
Tape device? This is overclock.net. Buying a tape device is blasphemy.
Edited by Manyak - 5/25/08 at 2:08am
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post #7 of 8
Thread Starter 
Quote:
Originally Posted by Chozart View Post
RAID5 is similar to RAID6, but with two parity stripes. I.E., two drives can fail.

Plus, with modern drives, what's the true failure rate? It's pretty darn low.

thlnk3r: LOL... if he wants 4-5TB, with SAS indeed you'll need an unlimited budget I think the largest SAS drive is in the ~300GB range, and hundreds of dollars for a single drive.

Have you thought about RAID10 or RAID0+1? In those cases, you can use the onboard controller (performance will be as good as RAID50 or RAID6 on a dedicated true hardware controller). You'll need eight (8) 1TB drives to get 4TB of storage space. With, for example, these Seagates, that'll cost you $1,679.92

The alternative is RAID50 with six of those drives on a dedicated controller. Six of the same Seagates will ring you up $1,259.94 and a decent controller card that supports RAID50 will cost you $449.99. Total cost: $1,709.93. Basically a tie, but RAID10 or RAID0+1 is much easier to rebuild in case of failure.

Personally, I do NOT recommend RAID for ANY important data... I'd highly consider a SINGLE external drive for your most critical data (or a tape device...). Then schedule nightly backups to that drive. The issue with RAID is that the moment you replace the RAID controller with another type, you'll have to rebuild the RAID array. Imagine that in a year or two your RAID controller bites the dust, and it's impossible to get a replacement. Ok, worst case scenario, but still.
Thanks for the info!

The price comparison is great... I think the raid controller is probably my best bet since I prefer running sata to my optical drives and my board only has 6.

As for my use, its not CRITICAL data, it would just be a pain to replace all of it (take months, etc). I'll pay the premium for the convenience.

I currently have about 2tb of data spread across 4 machines and external drives that I'd like to get in one place on the server to make it easier to access. So, I'll probably go with RAID5 as its better then no security and cheaper then 1/10 and controllers with RAID6 get pretty expensive...

Now to find a good external enclosure..

Thanks again!
post #8 of 8
Quote:
Originally Posted by Manyak View Post
Tape device? This is overclock.net. Buying a tape device is blasphemy.
Manyak, tape backups are still very common. A PV124T LTO2 from Dell coupled with Backup Exec can do wonders
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