Your RAID5 recover statement is incorrect. You only need 4 of the 5 drives
to recover. However, if 2 drives fail, all data is lost.


On Wed, Apr 3, 2013 at 10:04 AM, Carruth, Rusty <
Rusty.Carruth@smartstoragesys.com> wrote:

> Very good rambles!  See my comments (well, rambles) below.
>
> > -----Original Message-----
> > Subject: Re: Home Office Server Security
> >
> > semi-coherent ramblings follow - I wanted to give you some stuff to
> > consider
> >
> ...
> > Use whatever RAID you are comfortable with.  I've tried RAID5 and
> > RAID1, and RAID1 is by far the easiest to recover from.  RAID0 is a
> > disaster waiting to happen.  Some people have had no problems with
> > RAID5, but it seems almost as many find RAID5 such a PITA that they
> > swear "never again!"
> >
> > I did RAID1 with two drives bought at the same time.  Sure enough one
> > drive failed, and I was too busy to address it.  A couple months later
> > the other drive failed.  Duh!  Same drive manufacturer, same model,
> > almost same manufacture date - yeah, I asked for that.  You might want
> > to use different drive manufacturers to mitigate that risk.
> >
>
> Remember the theory behind RAID is that two 'independent' drives will
> fail at different times.  Is that a valid assumption? I'm not convinced
>
> The problem with raid 5 is that, in order to recover the array ALL
> DRIVES in the array must be 100% functional or your rebuild will fail
> and you lost your data anyway.  (of course, if you have more than one
> 'parity' drive then things are different).
>
> Raid 1 is similar, really, but may not be as fatal if you lose one
> block.  I've not tried it nor thought much about that, so I may be
> wrong.
>
> The purpose behind 5 is to save money, I think.  The question I have is
> - how important is your data?  If it's important enough to want to have
> redundancy, why is it not important enough to use RAID 1 with 2 OR MORE
> drives?  Too expensive?  Then be certain you have a good backup system!
> (Oh, my, look!  A backup system will be another copy of all your data.
> Taking the same space (or maybe less because of using gzip or other
> compression).  Wow, 2x the disk space! Saved lots of money, did we? :-)
> Of course, the backup system can be slower and cheaper drives... wait,
> how important was this data???)
>
> Rabbit trail: But the ability to restore a directory you 'oopsed' is
> probably worth the cost, and RAID doesn't give you that ability.
>
> So, in summary, I'm saying that almost all decisions are tradeoffs
> between cost, risk, time, and probably other stuff.  "You pay your
> money, you make your choice" :-)
>
> Rusty
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