> Alan K Baker wrote:
> >
> >
> > At a guess, I'd say that one other possible way is
> to buy a broadcast
> > quality camera with no internal recording and
> export the clips to
> > computer in real time. Obviously the PC is still
> using mechanical
> > components, but you can minimise data loss by use
> of RAID.
If you're going to use a RAID setup, the best way is
to use a seperate RAID controller card. That ensures
the ability to move the array to another computer and
also the ability to upgrade the motherboard without
having to re-create the RAID.
Many motherboards (especially ones with SATA) these
days have built in hardwware RAID support, but since
it's a non-removable part of the motherboard, it's
quite unlikely you'll be able to plug all the drives
into a different motherboard and access your data.
Another option is software RAID. Windows NT4, 2000, XP
Pro, Server 2003 and most likely some versions of
Vista have this ability built in. (Don't know if any
OS X version does. No pre-OS X Mac OS version does,
but there was 3rd party RAID software.)
Striping drives assigns storage blocks across multiple
drives, spanning files across them. The drives are
written and read in parallel, speeding up file access
in most cases. If one drive in the array fails, your
data is gone. Smaller files that had no chunks on the
failed drive may be recoverable by a specialty data
recovery company, if you want to pay them a lot of
money. This is called RAID 0.
Mirroring drives cuts your total capacity in half. It
uses at least two drives and simultaneously writes the
exact same data to both. If one drive fails you lose
nothing. This is called RAID 1.
The next level is similar to RAID 0 but adds
redundancy by dedicating one entire drive for parity
data. Any ONE drive may fail and the array will still
operate without losing data, though at a significant
performance loss if the failed drive is NOT the parity
drive. If the parity drive fails, then the array
operates as RAID 0 with no performance loss. If two
drives fail then it's sayonara data. This is called
RAID 4 or RAID 4. (Minor little differences between
the two.
Better than RAID 3 or RAID 4 is RAID 5. Instead of
using an entire drive for parity data, it uses a small
amount of every drive to store it. Performance is
better, it allows higher usable capacity for the same
number and size of drives, and rebuilding data on a
replacement drive is generally quicker than on a
failed data drive in RAID 3 or RAID 4. But as with
them if a second drive fails before the first failure
is repaired, *poof* goes the data.
RAID 6 uses dual distributed parity, scattering it
among the drives so that if any TWO drives fail the
data is still recoverable.
There are also RAID systems that combine two of the
others, called Nested RAID, but you're unlikely to run
into (or need) such complexity outside of really large
datacenter systems.
A word of warning on Windows software RAID in XP Pro.
What it calls RAID 5 is actually RAID 4! The Help of
RAID says a single drive is used for parity.
If you want RAID on the cheap, many older servers had
SCSI RAID controllers that can be pulled out and used
in desktop computers. I got a Compaq SMART-2DH card
and the drive cage from a defekt ProLiant 1600 server
and just for fun popped it into one of my XP Pro
desktops. *ping*! XP had a basic driver for it and
there was the RAID 5 array of five 9.1 gig SCSI
drives. I got the latest Windows 2000 (XP is NOT
supported on the ProLiant 1600, it'll install but MS
has rigged XP Pro to *not support* dual CPUs on that
model and several other 'big name' servers.) drivers
and array configuration software from HP. Works just
fine- as long as I keep a fan blowing on the
hot-running 7200 RPM drives.
I'm on the prowl for 1" tall SCA80 hard drives with
capacities larger than 10 gig. The SMART-2DH can work
with different size drives but the biggest single
volume is limited to the size of the smallest drive in
an array times the number of drives in the array. (It
supports more than one array per controller.)
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