RAID Recommendations

Posted on 2005-05-04
Last Modified: 2010-04-03

I have a database on RAID 0 which I conceed is a bad idea for a database.  

I want a RAID 10 setup - which is a second RAID 0 that you mirror (RAID 1) .

Question - at the moment my two RAID drives are Western Digital Raptor 10,000 rpm which are a little on the costly side.

If I purchase another two drives to make RAID 10, do you recommend that I go for drives of the same speed - or can I save a penny by going for cheaper drives.

What I am thinking is that if either of the Western Digitial Raptor drives fail, I can run on the slower drives for a short period until I install and restore the Western D.Raptor array.

However, performance on-going is key and therefore if purchasing slower drivers will impact performance of the whole array - I dont wish to go that way.....

What are your views?
Question by:amacfarl
    LVL 95

    Assisted Solution

    by:Lee W, MVP
    Don't be a penny pincher like that.  The WD Raptor drives are NOT that expensive.  It's not like you went SCSI.  

    With a Mirrored RAID 0, you'll just end up running at the slower speed drives speed all the time so the mirror stays in sync.  I just wouldn't risk it/reduce my speed for saving $50 or so.
    LVL 2

    Author Comment

    ha ha ...

    it is not a matter of penny pinching, in short i am starting up a business and dont wish to spend money needlessly.

    Standard 80GB SATA Drives = £40 each = £80

    whilst Western Digitial Raptor cost = £118 each = £240.

    so the saving is £160 (approx US$ 300)

    but based on your previous answer, going for the cheaper drives will impact performance....  

    However our database is read only 20 hours of the day - (we implement updates during a 4 hour window).  It may be worth purchasing the cheaper ones and doing a regular DB sync between the two arrays.


    many thanks

    SCIS vs SATA ;-)
    LVL 4

    Accepted Solution

    I'm with leew. Don't skimp on mismatched drives. Not only is there a performance degradation, you also are skimming a reliability issue.

    Raptors are simply made better than other drives. It's why they have MTBFs of 1.2M hours and get the fancy warranties on them. They're designed for extended usage. IIRC, average MTBF on most other SATA drives is less than half of that. so you won't have true redundancy and you'll have to plan to replace on set of drives at some point down the line anyways.

    Not to mention you've already made a commitment using relatively new tech. SCSI has a lot of things going for it and is fundamentally more efficient in drive access than SATA(rev 1 at least, won't know about SATA2 until it comes). storage systems is more than just the drives, it's controllers and backplanes all sorts of chips that support techs will charge you an arm and a leg for. I'm not saying sata is bad. Apple has made a huge commitment in the technology with their xsans, just that you should probably avoid injecting issues like this.

    It really boils down to exactly how much performance and stability you want from that system. what are the performance metrics for your app and what is the cost of downtime in the event of drive or array failure. In the end, you have to really decide what, if anything, you can sacrifice. Personally, I doubt the drive performance is your bottleneck (it usually isn't in a networked DB). More likely it's the network.
    LVL 95

    Expert Comment

    by:Lee W, MVP
    Interesting article, but I'd rather have all the details - including the SCSI cards and drive speeds used.  Otherwise, that review isn't much better than apple claiming a Mac is faster than a PC if the PC has 128 MB of RAM and HyperThreading disabled.

    That aside, The Raptor drives are based on SCSI drives - ever notice that SCSI drives are incremented in 9 GB increments whereas IDE/ATA drives are 10 GB increments?  SATA drives are basically a different connector attached to one technology or the other.
    LVL 2

    Author Comment

    In truth this is the article that I used to base my decision to go with SATA instead of SCSI.

    it makes interesting reading and provides a more balanced view on the topic than the previous one I inserted.

    Thanks ever so much for your replies and suggestions.  If one was to base the decision excluding cost, I think indeed the answer is to go for another two Raptor drives.  However the 'cost' question comes back always.  At the moment I am in the process of getting married and starting up a business, so as you can understand, money is on tap.

    Saying this though... poor reliability and long downtimes can be the recipe for killing a business before its feed leave the ground.  Thus for $300 bucks...hmm.  To be honest, I am going to have to sleep on this one before making a decision.  As Kooroo said... "It really boils down to exactly how much performance and stability you want from that system"

    Thanks to you both for your long and detailed replies.  As I have said in many occassions, I am always shocked and stunned by the efforts people go to answer my questions.  In my view the subscription for Experts Exchange is one of the best investments I made.

    All the best

    P.S I have shared the points between you

    LVL 55

    Expert Comment

    If the Raptors were mirrored and  then striped to a pair of cheap disks then you would get the same read and write speed as 4 slow ones since the raptors would have to wait for the others to catch up. If you mirrored a Raptor to a cheapo and then striped it to a similar pair write performance would be the same as 4 slow ones but read performance could be slightly better if the controller treated one disk in a pair as primary and only bothered to read from the slow disk if the primary was dead.

    Performance aside, like leew said the Raptor isn't a cheap SATA drive, you would be mixing something rated at 100% duty cycle with something rated at 25% and it sounds like your disks will be running 24 hours/day.

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