On Wed, 27 Feb 2002, Derek Chan wrote:

> If what they are selling is what I think it is, then you insert this card
> into your PC with a number of hard disks, example 4 hard-disk. If one
> hard-disk crashes, then information from the other 3 hard-disk can be used
> to regenerate the lost data.

Correct, assuming RAID 5.

RAID 0 - Striping.  Makes 2 or more disks look like one big drive, no
redundancy.

RAID 1 - Mirroring.  Keeps two copies of the disk on 2 spindles.  Full
reundancy.

RAID 3 & 4 - Forget the details, but they're not commonly used.

RAID 5 - Striping with parity.  A spare spindle is used for parity
information so you can lose one disk (and only one) without losing data.
Requires 3 or more disks.

Then there are combinations - RAID 15 is mirrored RAID 5 sets, etc. for
the truly critical apps & data.

I use RAID 1 mirroring in my Linux machine now.  No special controller
required, the drivers are bult into the OS.  Solaris and most other UNIX
flavors have this as well.

> I thought such things are availiable only for HIGH END COMPUTERS, and I am
> surprise it is avaliable for PC. Anybody tried this product before ? and Did
> I understand what RAID is correctly ?

Yep, you did.  I don't use the Promise controller, but a friend does and
likes it.  Actually he bought the ATA-100 controller and found out there's
one jumper to make it a RAID controller also, same hardware just a
jumper-seleted software feature that saved him some money.  He's tested it
(as I tested my software RAID); works perfectly.  Since they're IDE drives
there's no hot swap capability, but it's not a critical business server,
so no big deal.

I do high end computers for a living - UNIX front end systems manager for
a large online brokerage.  In a critical application we use either
mirroring or RAID 5 - depending on the space needed - then deploy two or
more identical, load balanced servers so if one fails we're still OK.  Of
course there is always the EMC disk arrays...  multiple TB of RAID5 space
that can be dynamically allocated.  Every house should have one!  8-)

Dale

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