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RE: [K12OSN] why RAID?



> I see a lot of posts here asking about setting up a RAID 
> system.  My ignorance and inexperience will no doubt show 
> through here, but why is it so important to get RAID set up?  
> Why not just have a cron job that makes a copy of /home or 
> any other important directories?  It could be set to run 
> every night, or even after every class period.  It could be 
> set with a low priority via the "nice" command so that it 
> doesn't interfere much with the read/write operations of 
> users who are currently logged in.

In addition to Jim McQuillan's point you also get the performance
benefits with RAID0 or RAID5 via striping.  Say with a single drive your
platters need to make a full revolution to write every bit of data.  If
you stripe with 2 drives you cut the time in half (theoretically), 3
drives into a third and so on.  Because while the first drive is making
is revolution after writing the bit the next drive has the ability to
write a bit etc.  

So bottom line is RAID1 and RAID5 get you redundancy with immediate
failover, no downtime.  And RAID0 and RAID5 gain performance with write
speeds.  My preference is RAID5 when possible because it gains the best
of both worlds, but unfortunately you pay more for the controllers that
handle it.  If you are on a budget crunch RAID0+1 in my opinion is the
next best option.  

And I personally never trust backups, they are my insurance.  But when
there is a server down and users on my back I want immediate results
that allow me to do repairs in the off hours, and leave the backups on
the shelf.

Another note is that with RAID0 you get the full total of all of the
drive amounts added together (80GB+80GB+80GB=240GB).  With RAID1 you
only get the total of the one drive (80GB+80GB=80GB).  And with RAID5
you loose the size of at least one of the drives in the raid (RAID5 uses
3 drives minimum)(80GB+80GB+80GB=160GB).  So RAID5 also makes the most
efficient use of your storage capacities while maintaining redundancy
and failover.

Also with RAID you can buy "Hot Swap" controllers and drive trays (at an
extra cost of course).  This allows you to remove the bad drive while
the machine is running and the RAID rebuilds itself on the fly.  Your
users never see a difference and your not in after hours.

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