Re: Newbie storage questions... (RAID5, SANs, SCSI)

"Nik Simpson" <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> IIRC, the original RAID definition for RAID3 is striping at the byte level,
> not the bit level, perhaps you are thinking of RAID2.


Both RAID2 and RAID3 are (effectively) striped at the bit level - the
smallest addressable unit ("sector" or "block") of the array is split
across all the drives, thus reading (or writing) that unit requires
hitting all those drives (hopefully in parallel).  What's different is
how the error correction works.  In RAID2 an EC scheme is used on a
bit-by-bit basis, in RAID3 you've got a block parity scheme just like
in RAID4/5.  I've never actually seen a RAID2 implementation, but it's
possible someone has one somewhere.

The point of RAID2/3 is to improve *sequential* I/O performance. 
Random I/O performance is that of a single drive, but sequential
performance is improved proportionally to the number of data disks in
the array.  Typically RAID3 arrays have the spindles synchronized for
best performance.  Mostly used by the HPC folks.