RAID 1 performance (was: ext2 Advice)

[jrv at vanzandt.mv.com (James R. Van Zandt)]

Derek D. Martin writes:

> You could just mirror the disk.  For most people, that's probably
> the easiest and cheapest way to go, once you get past figuring out
> how to make a disk mirror.  But then, there are nice how-tos that
> tell you exactly what to do...

I guess you're talking about RAID 1 here?  I'm thinking about that for
my next machine.  Here's what I had in mind:

  Adaptec 29160 SCSI controller
  two IBM 36 GB U-160 10k rpm hard drives, in software RAID 1
  Tyan S2466N-4M MPX motherboard

With software RAID, I recognize that write performance may be
somewhat poorer than with a single disk.  However, I'm hoping read
performance will be quite a bit better.  

Here's my analysis: The Ultra160 SCSI bus has a bandwidth of 160
MB/sec, which is more than twice the sustained transfer rate of a
single disk (29-57 MB/sec).  The Adaptec card uses a 64 bit PCI bus,
and the motherboard supports 66 MHz on its 64 bit PCI slots.  Does
that translate to 8*66=528 Mbytes/sec?  If so, it seems I should get
something like twice the data rate on reading as with a single disk.

However, all the Software-RAID-HOWTO promises is "a noticeable
performance improvement".  Am I missing something?

I'm also wondering how much noise those 10k RPM disks make.

	 - Jim Van Zandt