RAID 5 solutions?

[Lou Kamenov]

In some email I received from "Dimitris" <sehh at altered.com> on Mon, 25
Nov 2002 21:16:52 +0000 (GMT) :
> On Mon, 25 Nov 2002 08:41:52 -0600, Jonathan Belson wrote:
> 
> >Using SCSI would be a lot more expensive than IDE; does it have
> >any significant advantages for this application?  I'm not
> >expecting the machine to be pounding its harddrives 24x7.
> 
> From personal experience, IDE is bad.

Nope, IDE and SCSI drives structurally are the same, the bus
makes the difference. The IDE bus is built on AT bus interface, 
where the SCSI logic board uses extra SBIC chip.

> Several reasons:
> 
> 1) Bandwidth (ATA/133) is extremely lower compared to a U160 scsi
> controller. Adverts on tomshardware and other places show nice graphs
> and compare ATA/133 to SCSI as near equals, thats all lies in my
> experience.

Comparing donkey with a van eh?
I`d use SCSI if the drive has to operate with loads of data hungry
tasks. And i mean *really hungry* multitasking, not a Samba/NFS server
with 10 users.
 
> 2) CPU usage. Even though their advertising says the opposite. They
> use A LOT of cpu. So don't be alarmed to see a huge increase of cpu
> usage.

Yes, a SCSI controller is able to control everything without any work
of the processor. However I disagree a bit with that. "A LOT"


> 3) They are NOT REAL hardware RAID. They require software to operate,
> and i dont mean the management software, i mean that the DRIVER
> actually does half the raid work. In SCSI raid, the operating system
> only looks at a single harddrive, it doesn't care if its raid'ed since
> the controller does all the raid work. I call this cheating and their
> advertising should mention that the driver does half the job (but
> thats why they are cheap...).

Sort of.
Basically all the drives on the SCSI massive are able to operate at the
same time, with IDE the things are a bit different, it`s limited to a 2
drives in a massive which cant operate at the same time, hence they must
take turns.

> Ofcourse an ide raid controller are considerable cheaper, so take your
> pick.

Right.
However we all know the MTBF of a SCSI. 
You`ve to ask yourself, do you really need SCSI?!


---
Lou Kamenov	lou at freebsd-bg.org		lou at seclab.aeye.net
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