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Raid 5 vs Raid 1 - Whats the best for a PDC?

Posted on 2006-06-21
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Last Modified: 2010-04-03
HI!
trying to replace my current PDC (windows 2000 advanced server) and debating to go Raid 1 or Raid 5.

It will only be used as the PDC and we have about 125 servers/pcs on our WAN.

Can you list the goods & bads of ea? and recommend?

Thanks!

ST
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Question by:ststst
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Expert Comment

by:Lee W, MVP
ID: 16955896
There is no such thing as a PDC in Active Directory (Windows 2000/2003).  Everything is a DCs.

You simply don't need that much space for a domain controller.  A RAID 1 should be more than sufficient.

Of course, you SHOULD have TWO DCs to protect against failure.
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by:fruhj
ID: 16955917
Raid 1 is cheaper, only needs 2 drives. Support is part of almost every motherboard out there now.
Cons: Raid 1 is not expandable - a mirror is a mirror

raid 5 often requires a special controller card, requires 3 drives (or more)
pros: Raid 5 can be expandable with the right controller, without needing to reinstall the server OS.

For a file server, database server, or mail server, I would reccomend raid 5.
For a fixed purpose server like DNS, PDC etc.. (where data volume is likely to never exceed the drives) then Mirroring is a fine way to go.
Note that you can also do mirroing in software, but You are far better off to do it at the BIOS/controller level,
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by:VortexAdmin
ID: 16955935
How many drives do you have or how many do you want to buy.  RAID 5 is faster but doubt it'll make that much of a difference.  I'd say save your money and go with RAID1 unless you ever intend to do anything else with the server.  On a network of 125, it seems a standalone DC would be kind of a waste anyway.  

The only bad to RAID 5 in comparison to RAID 1 is it takes more drives and sometimes more expensive hardware.  I guess gives off more heat could be another con since there's more drives but I'm guessing that won't matter to you so much.   Other than that it should be faster and more reliable.
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LVL 44

Expert Comment

by:scrathcyboy
ID: 16956085
RAID 5 is prone to failure on disk loss or removal.  If you want a secure RAID with backup in the event of a failed disk or a removed/reinserted disk, by all means use RAID 1 -- a little slower, but worth it, in that each disk is a mirror, and independently sustainable regardless of the other disks condition.  I have lost many RAID 5s by removing and reinserting disks, but have never lost a RAID 1 array yet.
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Assisted Solution

by:seehear
seehear earned 25 total points
ID: 16962127
The main benefit to RAID 5 is read speed and data reliability.  If you use a good _HARDWARE_ RAID5 solution you will be able to recover from any of the drives dying with little drama.  In fact, enterprise RAID controllers will allow you to specify a hot spare that will automatically take over if one of the live drives goes down.  The down side to RAID 5 is space for dollar: you "lose" the capacity of one drive to parity. In other words, three 500 Gb drives will yield 1 TB; four drives will yield 1.5 and so on: Yield = (drive size x number of drives)-drive capacity.  Also, write speed suffers some what, compared to a RAID 1 config, but read speeds, especially multiple concurrent requests are much faster with the RAID5 config. For "normal" use SATA drives are fine, for high demand applications, use scsi drives - available up to 15k rpm spindle speeds.

I'm not sure what type of hardware and configuration scrathcyboy was using when he lost his data, but I would say my experience (more than ten years as head geek) is exactly the opposite of his: RAID5 is very good because it survive disks dying or being removed. Of course, you do have to know what you're doing , lol. And, I don't recommend software RAID5 solutions.
In enterpise environments, RAID5 is the most common configuration you will find for the reasons I specified.

When I build a server I use one physical drive as the system drive and (at least) 3 in a RAID5 config.  Details of equipmenrt and configuration vary by application,but these are from one I built recently to serve media: 1 raptor for the system drive, 3 seagate 750 gb drive in RAID5 to yield slightly less than 1.5 TB of filesystem space. The client wants the most reliability for her music collection of over two thousand albums (and growing), all ripped from her own CDs, an effort she is not interested in repeating.  It is overbuilt, to be sure, but she will not have reliability or saturation issues on her gigabit ethernet network.  I am a little concerned with the seagate drives because they seem to run very hot, but so far so good. Use plenty of fans and make sure cool air is available to the machines.

Hope this gives you the info you need to make the right choice for your application.

Regards,
James
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Accepted Solution

by:
VortexAdmin earned 25 total points
ID: 16964651
My only disagreement with the last post is that the RAID 5 space per dollar is better than RAID 1, not worse. It's true that you lose the capacity of a single drive to redundancy but you do with mirroring (RAID 1) as well.  And if you want to expand a RAID 5, you still only lose 1 drive to redundancy no matter how many you add.  If you have multiple mirrored drives, you would lose half of your total to redundancy.  So in comparison to RAID 1, this is not a downside.

For a DC I would not use a seperate system drive with RAID 5.  Put 3 drives together in a RAID 5 and partition a seperate virtual drive for the system files.  That way you have redundancy through the entire system which means no downtime during any drive failure.  That being said, I think I'd still save my money and go with RAID 1 for your purposes.
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by:VortexAdmin
ID: 17236690
Did you not agree with our comparisons of RAID 1 and RAID 5?  Curious why you thought our answers deserved a grade of B.  You asked us simply to list the pros and cons and make a recommendation.  Not sure how you can even grade a recommendation?  With all the responses, was there information you think was left out or was not answered correctly?
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