SCSI Disk/Controller advice please

Jason Gurtz jason at tommyk.com
Mon Nov 1 08:27:16 PST 2004


On 10/29/2004 20:08, Joao Clemente wrote:

> 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?

You should definitely go with hardware RAID if you have the extra $$.  It
just makes it so much less problematic when something happens and you have
to replace a drive, etc...

One thing to look for is if your server motherboard supports a zero
channel raid card.  That means the motherboard has a scsi controller
already and then you put in the raid card which is either a SO-DIMM format
or PCI card.  The card will have the cache memory and the raid processor.
 The newer Adaptec stuff is all very well supported under Linux and
FreeBSD as opposed to their old ARO/AAA line.  See:
<http://www.adaptec.com/worldwide/common/index.html?prodkey=linux_home1&source=home>
In the Linux kernel they are using the I2O or aacraid driver.

an ultra160 card will have more than enough bandwidth for two drives that
are mirrored, even if they are top of the line 15K RPM drives.  an ultra
160 controller (or even ultra80) will work just fine with ultra320 drives.
 It's all LVD signaling now so the speed will be at whatever the slowest
component is.  Check out the adaptec 2110S or 2120S controllers if you
don't have the zero channel capability.  The Intel cards are OK too and
support Linux as well as being a little cheaper than the adaptec cards

> 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?)

It is a controller feature but most do support it.  You also to have a
case with a scsi backplane that uses SCA connectors (80-pin).  This is
more expensive...  Plain old 68-pin drives and scsi cable w/ active
terminator work just fine if you don't need hot plugging.

> I'm quite confused about all the SCSI variations..

The only show stopper would be if you get a scsi cd-rom drive or tape
drive that has a 50-pin connector.  This uses SE signaling and only
supports SCSI ID's less than 7 (controller is usually ID 7) whereas LVD
devices support up to ID 15.  I use 68-pin to 50-pin adapters to hook a SE
DAT tape drive to the LVD bus.  The adaptec controllers have no problem
with this, but some other, older controllers will slow down the whole bus
to the speed of the slow tape drive's interface.  Most new SCSI tape
drives now come with LVD interface so this isn't a problem anymore

> 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?

I liked the Seagate ones for a while but now recently I've been using the
Maxtor (used to be quantum) atlas IV drives (10K rpm).  I've never used
the Fujitsu drives.  You may want to check out:
<http://www.storagereview.com/>  for good, impartial performance testing
of drives.  Unless you really want to spend a lot, 10K rpm drives will
probably be more than fast enough.  10K drives run cooler too  :)

> - 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)

Be careful if you see the term "Host RAID" this is not true hardware raid.
 It is software raid that is done in the scsi controller driver.  The
newer adaptec scsi controllers support this and incidentally this also the
type of raid you get with nearly all SATA controllers!  Real hardware raid
controllers have a risc co-processor on board which does the raid
calculations.  It can be more cost effective to get a motherboard that
supports a zero-channel raid controller.  Just be sure to get the right
model because there are 32-bit PCI (old), 64-bit PCI, PCI-X (this is not
PCI express!), and SO-DIM form factors.  Even the 32-bit PCI bus will have
enough bandwidth for a plain mirroring situation so don't worry too much
if you're not running on PCI-X 64-bit/133Mhz.  Supermicro server boards
are good, as are the Intel brand ones.  Check out the SE7210TP1SCSI model
from Intel with the SRCZCR raid card.  Be sure to check out the Tested
hardware and OS compatibility list *before* purchase.  Supermicro has the
nice P8SC8 motherboard.  For raid vendors LSI Logic and ICP Vortex are two
more good ones to look at.  CBL-034-U320

Any modern controller will always have 68-pin internal connectors.  If you
do hot swap, you would use a 2 connector 68-pin cable to go from
controller to backplane.  the backplane is a fairly simple circuit board
with 80-pin connectors for the drives.  Make sure that the scsi cable has
active termination.  Most of the motherboards that have scsi built in will
come with the proper cable now-a-days but you have to be sure.  Most
backplanes have the termination built in  Call and ask for pre-sales
support before purchase  :)

Cheers,

~Jason

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