RAID 5 solutions?

Paul Robinson paul at iconoplex.co.uk
Tue Nov 26 13:13:34 GMT 2002


On Nov 26, Lou Kamenov <lou.kamenov at aeye.net> wrote:

> 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.

Which, it has to be said, makes a whole world of difference. In the past 
I've had various issues with SCSI, Fibre channel and IDE setups. They all 
have their advantages and the flips sides as well of course.
 
> 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.

We use SCSI when we want RAID - full stop. IDE RAID is fine, but it just 
seems clunkier. Oh, and of course we use SCSI for the tape systems.
  
> Yes, a SCSI controller is able to control everything without any work
> of the processor. However I disagree a bit with that. "A LOT"

It's relative, and depends on the processor. If a processor is going to 
spend say 'X' thousand instructions a second dealing with the disk, as to 
whether that constitutes "A LOT" depends on how many instructions a second 
the processor can do total. Sure, you might not notice much with a P4 2Ghz 
machine, but if all you have is an old 486SX and you're trying to run X at 
the same time...
 
> 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.

Which is one of the several reasons they are clunky, nasty and not suited to 
RAID, IMHO. Although you can build a few terabytes of storage for less than 
£5k these days, which is nice if you just want a backup server.
 
> Right.
> However we all know the MTBF of a SCSI. 
> You`ve to ask yourself, do you really need SCSI?!

I've never had a SCSI disk fail on me. Seriously. Perhaps I'm out on the 
95th percentile to the 'M' in MTBF. ;-)

Just going back to the terabyte stuff above, some of you who are looking at
large RAID solutions might want to take a look at the
NAS/SAN/Direct-attatched stuff under the "Teravault" name that they're doing
at dnuk.com - it looks decent kit and the pricing isn't bad (3.2TB for less
than £10k + VAT). I've had server kit off them in the past (including the
one I'm writing this on)  and it's high-quality stuff.

-- 
Paul Robinson




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