Re: [K12OSN] SCSI Disk subsystems was: Building a new lab server...recommendations?

["Terrell Prude', Jr." <microman cmosnetworks com>]

This depends on the number of disks you have as well.  I was running 
six- to 14-disk arrays at the time.  Also remember, real-world file 
systems often have lots of "little" files (read: < 500kB) all over them, 
especially user home directories.  If you were copying, say, CD-ROM ISO 
images to an uncluttered, pristine filesystem, you would probably see a 
much higher number, likely close to the limit of what your PCI bus can 
take.  That's why most higher-end RAID controllers are 64-bit PCI 
cards.  If you're doing file copies from what I would call a "typical" 
file system, then that's a different matter.  Yes, striping across 
multiple spindles certainly helps, but read/write head actuators moving 
around all over the place will still be a factor.  It depends on what 
you're moving around.  That's why I laugh every time the IDE or SCSI 
camps come out with something with some insane spec (UDMA-150, U320 
SCSI, etc.) that applies only to the electronics, not the physical 
disk.  Ultra2-SCSI controllers are, in my experience, more than sufficient.

As for the hardware RAID controller, it is a good thing if you, say, 
have a K12LTSP server with a bunch of people running the GIMP, Mozilla, 
or SPICE (or some other CPU-hungry app).  Software RAID eats up some 
CPU, and the sysadmin may want to devote as much CPU to the apps as is 
possible.  For shops running SPICE or doing graphical rendering, CPU 
time translates into money really fast.

--TP

Immanuel Derks wrote:

> Op di 01-04-2003, om 06:53 schreef Terrell Prude', Jr.:
> Sounds very reasonable to me and exactly my findings concerning single scsi channel raid setups: I have seen respectable performance in good relation to bus width and amount of disks
> attached.
> That's why I'm so confused to have only 47MB/s on a single channel scsi-320 Raid0 setup with a hardware SeveRAID-5i controller (128MB cache).
> Disks also scsi320 15000rpm 'course.
> It should scream at least double that speed otherwise it is simply not worth the investment and besides the point having hardware raid controllers.
> It would then be more interesting financially,performance wise and for redundancies sake to do software raid on two channels.
> I just hope my controller is broken to account for the abominable bad performance....(do we keep on trusting IBM hardware?)
>
> Alla, still hope some scsi320 server out there with a hardware controller on a single channel raid setup can push some hdparm's to the list :)
>
> Kind regards, Immanuel
>
>
>
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