Re: SCSI Disk/Controller advice please
On Sat, 30 Oct 2004 00:01:43 +0100, Joao Clemente <jpcl@rnl.ist.utl.pt> wrote:
> Hi.
> For the first time I'm gonna setup a server with SCSI disks (until now
> I've done it only with IDE - regular ATA or SATA)
>
> I'm getting a completly new server (P4 3Ghz, Dual-Channel DDR 400, MB
> with intel chipset) and, while I have a good ideia on these components,
> I would like to setup a RAID-1 system with SCSI disks...
>
> I'm looking for advice on these: wich scsi controller should I buy?
> Software or Hardware RAID-1? Wich disk brand? (I'm getting a couple of
> 36GB, it is more than enough space for my setup)
Linux software RAID is usually good enough, but since you already
invested a lot in SCSI, go for the hardware RAID. There's a recent
thread in this mailing list concerning hardware vs software RAID.
There are a lot of good hardware RAID cards to choose from. On a lot
of enterprise machines you'd get good ones by default. Linux has quite
a good sizeable roster of supported SCSI chipsets.
> Which are the tradeoffs of hard vs software raid1? What happens/How do
> we proceed if 1 disk fails (how do we know it, how do we replace/resync
> them?)
The card's custom chip does the computing on hardware raid setups,
while software raid taxes the cpu for the computing. Otherwise, it's
almost the same.
When a disk fails, the other part in the RAID 1 (mirror) setup takes
over. It'll be preferrable if you could replace the disk once it fails
though - which is why hotplug is really a preferred feature.
Do note though that RAID 1 won't help you that much - it's better if
you could try higher RAID levels (RAID 5) for data integrity. RAID 1
will only mirror disks - and that would also mean should there be
errors in one disk it gets propagated to the mirror as well.
> This server can be shutdown for maintenance at off-work hours, so I
> don't need any hot-plugging capability.. (this is a controller feature,
> right?)
Yep. Usually hotpluggability is already built-in in a couple of SCSI RAID cards.
The good thing with hotplug is that when one disk fails, you could
replace it on the fly. Another thing I haven't tried is to do hotswap
on Linux software raid (though I've done hotswap on hardware raid with
no problems).
> I'm quite confused about all the SCSI variations..
>
> This is what I've found so far are somewhat like this:
> - SCSI disks, all Ultra320Wide:
> Seagate Cheetah 10K 68 pin, 36Gb - 160 EUR
> Fujitsu 10K 68 pin, 36Gb - 150 EUR
> Fujitsu 10K SCA/80pin, 36Gb - 150 EUR
> Fujitsu 15K 68 pin, 18Gb - 185 EUR
> Fujitsu 15K SCA/80pin, 18Gb - 185 EUR
> Ok, no problem with these... any brand/model suggestions?
> - Controllers
> Several Adaptec SCSI Cards from 200 to 400 EUR, wich can have:
> - 32 or 64bit
> - 160MB or Ultra320
> - Raid (or not, when they say nothing.. I think) (the RAID ones start
> at 400 EUR and I've seen up to 950 EUR)
>
> I'm confused... none of the descriptions of the Adaptec controller I've
> seen state the connectors (68/80 pins)... now add more controller to the
> mess:
The PCI bus has two variations - 32bit PCI (the short one found in
most PCs), and the 64bit PCI (the longer ones found in servers).
There's also PCI-X. You can safely guess that in terms of bus speed it
goes this way: 32bit PCI < 64bit PCI < PCI-X.
SCSI-2 disks have an 80-pin setup. SCSI-3 disks have a 68-pin setup.
SCA in SCSI just integrates the data and power wires to a single
attachment (hence Single Connector Attachment)
> Tekram PCI DC395UW - 56 EUR
> Tekram PCI DC390U2B - 102 EUR
> Tekram PCI DC390U2W Ultra 2 Low WIDE SCSI - 126 EUR
> Tekram PCI DC390U3W Ultra 3 WIDE SCSI 160 - 182 EUR
> Tekram PCI DC390U4W Ultra 4 WIDE SCSI 320 - 223 EUR
>
> Damn... Really confused... Please confirm these toughs also:
> UltraWideSCSI = 68 pin ... What is "2", "3" or "4" ?!? These seem
> "similar" to ATA 66/100/133 - the bus speed, is that it?
> So, what's SCA? None of these controllers says SCA...
Ultra-Wide SCSI = SCSI-3. For the other definitions - see my post above.
I think the 2/3/4 has something to do with the data rate. At any rate,
to really take advantage of ultra-wide SCSI you'd need to have 64-bit
PCI slots or PCI-X slots, as 32-bit PCI would cut down performance
sharply.
> Any help?
>
> Ps: I supose getting a SCSI crontroller built-in on the motherboard is
> stupid? Those are low-value/performance controllers?
Not all of them are low-value/performance connectors. Some are of very
good quality. You could always check the chipset used and ascertain
from other sources if the chipset is good enough.
--
Paolo Alexis Falcone
pfalcone@gmail.com
Reply to: