Pegasus R6, only use 4 drive raid

Discussion in 'Mac Pro' started by ogs, Jun 11, 2012.

  1. ogs macrumors member

    Joined:
    Jan 26, 2012
    #1
    Hey guys,

    Just wondering if it's possible to use 4 of the 6 drives in the enclosure in a raid 5 setup, and then two other ones working independently too?

    So on my computer I'd see:
    Drive 1
    Drive 2
    Drive 3 (4 drive raid)
     
  2. philipma1957 macrumors 603

    philipma1957

    Joined:
    Apr 13, 2010
    Location:
    Howell, New Jersey
    #2
    yes. but raid5 has issues known as writehole . i run 2 sets of raid0 and 2 single drives been flawless since nov
     
  3. ogs thread starter macrumors member

    Joined:
    Jan 26, 2012
    #3
    What's the best way to protect data via raid
     
  4. philipma1957 macrumors 603

    philipma1957

    Joined:
    Apr 13, 2010
    Location:
    Howell, New Jersey
    #4
    not sure what your needs are nano frog is a site member that has alot of knowledge on this matter . he may chime in soon
     
  5. ogs thread starter macrumors member

    Joined:
    Jan 26, 2012
  6. deconstruct60, Jun 11, 2012
    Last edited: Jun 11, 2012

    deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #6
    RAID 6 doesn't get rid of the write hole problem. If anything it makes it worse since there is even more data to write to several different platters to complete the write operation transaction.
     
  7. ogs thread starter macrumors member

    Joined:
    Jan 26, 2012
    #7
    Hmmm then which method would be best for 4 drives in an array for safe storage
     
  8. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #8
    The user manual can be downloaded.


    http://www.promise.com/support/down...SeriesSn=47&ModelSn=118&m=93&region=en-global

    Around Page 55 is "Creating Disk Array and Logical Drive with the Wizard".

    You probably want Express or Manual option. On express, 3 logical drives. one with redundancy+capacity+speed with no spare (should get you RAID 5) and two more logical drives with no redundancy, max capacity , no speed , and no spare . Or just manually spell all that out.
     
  9. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #9
    Yes, this is possible.

    Any particular reason for focusing on the Promise Pegasus products?

    I ask, as it's reliability isn't really known (Promise in general does well, but this product isn't very common in the field yet), and other solutions may be a better fit (i.e more flexible/better tailored to fit your specific needs).

    You'd need to sit down and figure out what you actually need, and consider the answers to such questions as the following:
    • How much capacity do you need?
    • What sort of throughput do you need?
    • How much redundancy do you need?
    • What kind of backup system are you planning to run (keep in mind, RAID is not a substitute for a proper backup solution)?
    • What about future expansion?
    • Budget?

    As previously mentioned, RAID 6 does not eliminate the write hole issue (write hole issue exists in any traditional parity RAID level).

    That said, there is a solution, but it's hardware based, which is why you need a proper RAID controller to deal with it (software based implementations of traditional parity levels cannot handle this issue at all).

    Another thing to consider is a good UPS system.
     
  10. deconstruct60 macrumors 604

    Joined:
    Mar 10, 2009
    #10
    If safety is absolutely the very top priority then ... RAID 6 is slightly better.

    Both can survive if the right two disks fail at the same time. In RAID-10 if both mirrors of one of the stripes fail you are lost. If the failure only occurs once in all the stripes (two in this case) then you are OK.

    In RAID-6 the parity and data is spread out a bit more between the disks.


    So a RAID-6 with the Mac and drive hooked to a battery back-up which would trigger a shutdown if switch to battery power for more than a minute or so. If that blows the budget then RAID-10 isn't bad. Keeping just the drive powered up with battery back-up is OK if know can get power back on before the battery runs out. That's not always possible in small shops or even big ones ( data centers near World Trade Center were without people and power for over a day and disk systems with batteries crapped out anyway. )


    Both are about the same usable capacity. You get the capacity of two of the four disks used.
     

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