Re: SCSI Disk/Controller advice please
On Sat, Oct 30, 2004 at 12:01:43AM +0100, Joao Clemente 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)
>
> 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?)
>
> 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?)
>
> 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:
n Sat, Oct 30, 2004 at 12:01:43AM +0100, Joao Clemente wrote:
> 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)
The controllers by Mylex, LSI and Adaptec all work well. Make sure it
is supported by a plain vanilla linux kernel.
> 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?)
Software raid eats up more CPU, but linux' software raid seems to be
rather good. Doing the root filesystem on raid in linux is kind of a
PITA.
> 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?)
Well that means you can simply buy 68 pin disks. The SCA disks are hot
plug and require a backplane ($$$).
> - 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?
Any of the 68 pin drives will do.
> - 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)
Any u160 controller will do so long as it is supported by linux. With
a two drive raid1, ultra 320 would be a complete waste of money (just
two drives cannot even approach using all that bandwidth).
> 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...
You would be looking for a hardware raid controller, with one channel,
two ultra 160 68 pin disks, and an LVD 68 pin scsi cable with a
terminator attached. A regular 68 pin SE cable will not do.
Now raid one is really for redundancy, not performance (though it
performs fine). You get best performance when separating filesystems
on different sets of drive spindles. for e.g., for a webserver (in
debian), you might set up /var on one raid array, and everything else
on another.
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