redundancy of SCSI controllers possible?

[Christophe Dupre]

> I'm talking about writing, not reading. If you have two disks on each
> controller, if one controller fails those disks won't be updated, but
> the others will. So the info is only partially written, and I'm not
> sure the data is there. Or is the raid code smart enough to detect
> this? If so, controller failure isn't a problem at all.

Then you are right, a controller failure will break the synchronisation. 
Hopefully, nothing a fsck will not fix.

>  >> Is it possible to put two controllers on the same bus, and if one of
>  >> them fails the other keeps with all disks?
>  >
>  >IF the aim is to make sure that the box can stay up with single controller
>  >failure I would make sure I have enough controllers to never put more than
>  >one disk per RAID set on each controller. 
> 
> This isn't possible, there aren't enough PCI slots.

Then go with a RAID hardware. If you must have the ultimate redundancy, go 
with two hardware raids on two controllers, and do a RAID-1 software between 
them. Make sure the two controllers are on separate PCI bus (high-end servers 
DO have multiple PCI bus).

Also, using a high-end box with, say, 6 PCI slots, you can have 6-disk RAID arrays, with one disk per array on each controller. With the latest 18-gigs disks, it will give a 90-gig array, if using RAID-5, which isn't bad...
-- 

Christophe Dupre
Analyste de systemes, 
RISQ inc.
550 Sherbrooke ouest, suite 250-ouest    Tel: (514) 845-7181, ext 237
Montreal, QC CANADA                      FAX: (514) 845-8083

"Nous ne sommes pas libres de ne pas etre libres, nous sommes obliges de 
l'etre"  -  Fernando Savater




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