[Nottingham] Large disks and storage

[Jim Moore]

@Camilo: I wouldn't count on anything short of an offsite mirror for
data security - what if there were a fire? Any backups you have would
suffer the same fate as your working system if the building were
gutted*.
For integrity against a disk failure, that depends a lot on the setup:
one disk failing in a JBoD stack would mean the loss of any and all
data on that disk, permanently. Failure of one side of a mirror is
recoverable, just pray that something doesn't go wrong while the array
is rebuilt (which is likely since a rebuild pushes the mechanics of
all drives in any array to their limits). Same as for RAID5, except
RAID5 isn't nearly as wasteful as a RAID1 (mirror) and the fact that
it utilises a (single) set of distributed parity data means that in a
single-disk failure, chances are good that if no other problems exist,
*no* data is lost. A RAID6 uses *two* distributed sets of parity data,
hence can (theoretically) lose up to 2 of the disks in the array
before any data loss occurs. This is a huge plus on the side of RAID6,
and I'm actually surprised to see a distinct lack of it in most
enterprise class server literature as an option.

*My data might be just movies and music and several thousand
photographs, but every so often I ship out an incremental update to a
mirror which is located in a different /city/. Call me paranoid, but
nothing short of a global thermonuclear war or the unlikely event that
the storage at both ends is otherwise suddenly and catastrophically
compromised will deprive me of my Armin van Buuren!

On 9/9/09, Sergiusz Pawlowicz <sergiusz at pawlowicz.name> wrote:
> On Wed, Sep 9, 2009 at 08:22, Camilo Mesias<camilo at mesias.co.uk> wrote:
>> It should stand to reason that there are more disks so more chance of
>> an individual disk failing - but less chance of losing any data
>> overall.
>
> one funny thing. i usually do raid1/raid10 using two drives. recently
> one of my drives failed, after 3 years, and i have fortunately
> replaced it quickly, because the one from this pair broke just 10 days
> after previous one!  it looks it is good idea to buy different drives
> with similar parameters for raid purposes.
>
> s.
>
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