Re: RAID 0

On Tue, 12 Jul 2005, E. Bond Francisco wrote:

> Hello Magnets,
>
> DP G4 800 Quicksilver
> 1G RAM
> OSX 10.4.1
>
> I'm looking for advice. I'm thinking I'd like to set up a RAID 0
> configurationon my G4, using 2 Maxtor 250G internal drives, for audio/video
> work with Final Cut Studio Pro.
>
> I have a Sonnet UATA133 card installed to accommodate the large size drives.
> My thought was to install the two new drives on that bus (is that correct
> terminology?), to configure it using Apple's software into a RAID 0
> (striped).

It's theoretically correct for Parallel ATA (PATA), since it is a
two-drive bus technology. Most PATA controllers have two busses (or
buses, or what SCSI controllers often call "channels"), which are often
referred to as the "primary" and "secondary." Some systems will only boot
off of the "primary" channel. (Note that it's not correct to refer to
SATA as a bus, since SATA is individual point-to-point drive connections.)

> I would then install my video/audio apps on this one drive, and
> keep my audio video files there as well.
>
> I would keep my other apps and system software on a 120G drive on the main
> bus (again, I'm not sure about the bus terminology), along with a second
> 120G drive. I use SUPER-DUPER to clone the system/apps drive to a 120G
> external.

So it sounds like you're going to have two RAID 0 drives on the secondary
channel and your main OS/app drive on the primary. So far so good.

> Questions:
>
> 1) How does one back up a RAID 0 configuration? I'm thinking I would need a
> single 250G drive to serve that purpose, and I would use SuperDuper to clone
> the RAID 0 to the single 250G drive. Is that the right way to do?

A quick RAID overview (because I always forget this):

RAID 0: two drives concatenated into a larger volume (roughly the sum of
the two drives). If the drives are the same size, then the RAID mechanism
will generally stripe data across the drives in an interleaved fashion for
increased write and read performance (in general).

RAID 1: simple mirroring of two identical drives

RAID 5: redundant striping of three (or five) identically-sized drives for
a capacity that's about 2/3 (or 3/5) the size of all three drives put
together.

I am conveniently ignoring RAID 4, 0+1, 10, etc. for the purposes of this
discussion. So if you're doing RAID 0 with 2 250g drives, you're going to
end up with a 500g drive. You may therefore exceed the capacity of your
extra 250g backup drive.

> 2) Would it make sense to install a system on the RAID 0 drive as well as
> the video apps and files, so I could make it a bootable drive? What are the
> pros and cons of that.

The big disadvantage of RAID 0 is that you get no redundancy. In fact the
overall reliability of the volume is _less_ than with a single drive
because you now have two single-points-of-failure in the two drives. If
just one drive fails, the entire volume is toast. So wouldn't do RAID 0
for the OS drive unless you're prepared for a long and painful restore of
your system drive if something goes wrong.

> 3) Finally, I notice that Sonnet also makes an ATA133 RAID pci card. I
> assume that's "hardware" raid vs "software" raid that I'd get from Apple. Is
> that a valid assumption?

Probably. Hardware RAID is super-easy to configure, since you configure
the volume in the firmware menu of the RAID controller and the volume
appears to the OS as a single drive. It also performs well. If you're a
real purist, though, you might want to plex the volume across two
controllers, each with its own drive(s). That theoretically yields the
best performance and reliability, since if one controller fries, you can
still run off of the second controller. This sort of configuration
_usually_ requires software RAID, since the volume spans multiple
controllers, although I think it might be possible with certain types of
enterprise SCSI controllers (anyone else know?). Hardware vs. software
RAID used to be one of those less-filling/tastes-great kinds of endless
arguments, but that seems to have died down, perhaps just because people
got too tired of arguing.

Hope that helps.

michael

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Received on Tue Jul 12 14:27:37 2005