[azipa] Can't build large SCSI array

[Reid Ferguson]

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Why are you trying to Mirror 10 Drives? This requires 100 percent
duplication of resources or N + N. (To mirror 5 drives it takes 10
drives) Although you need at least three drives, RAID 5 (data striping
with EDAC) is N + 1. Or, to Mirror five drives you need six. Now, add a
seventh drive and make it an on-line standby so when a data drive fails 
the 7th is automatically rebuilt with the data from the failed drive. 
Most major server manufacturer's support this configuration. The only 
issue here is the possibility that if two drives failed at the same 
time or at least before the stand-by drive gets built in the image of 
the failed drive the result would be catastrophic.

In either case you cannot get away from doing tape backup just because
you are running a massively mirrored configuration. What happens if a 
virus strikes and contaminates your data? What happens if a disgruntled 
employee decides to do a recursive delete on your data? 

The above configuration combined with a faithfully executed 
Grandfather-Father-Son backup routine makes a lot of sense for a 
lot of situations. 


Reid


Trent Shipley wrote:
> 
> We are having a terrible time building an array of SCSI disks.  It will
> consist of 10 physical drives, but they will be mirrored--so there will only
> be 5 logical drives.
> 
> We are using an AMI Elite 1600 controller with 37 Gbyte IBM Ultra LVD's
> (SCSI-3).
> 
> What happens is that any attempt to build the array fails when we load
> channel 1 (the second channel) with more than three drives.  (Channel 0 is
> happy with 4 drives.)
> 
> Calls to AMI have resulted in the usual tech-support purgatory.
> 
> We have never gotten to the point where we can install the operating system.
> So far the problem has consumed on the order of ten or twelve man-days with
> little or no progress.  The system is scheduled to ship Monday.
> 
> The problem is exacerbated by the fact that we are a small company, and no
> employee has ever installed more than four drives on a system.  In fact, no
> employee recalls having ever MET anyone who has set up a sizable disk array.
> 
> Free advice will be much appreciated.
>    Offers of fee-for-service advice will be considered.
> 
> Trent Shipley
> 
> Work:
> (602) 522-7502
> mailto:tshipley@symbio-tech.com
> http://www.symbio-tech.com
> 
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