[ILUG] Followup 1: Naive ADSL/WiFi questions (long (sorry!))?

[Michael Watterson]

paul at clubi.ie wrote:
> On Sun, 19 Aug 2007, Michael Watterson wrote:
>
>> In reality between a Workstation and a server HW RAID 5 (3 x 10K RPM 
>> Ultra Wide & Fast)  dual PIII 933MHz (with 512M RAMBUS memory) we can 
>> get sustained 30Mbyte/s using 1Gbps cards via the switch,
>                         ^^^^^^^^^
>
> So probably a PCI 33Mhz/32bit bus is the bottleneck there somewhere.
>
> regards,
Dunno, but apparently that's a normal sort of speed to see unless you 
have dedicated CPUs and   DMA controllers on the ethernet card. There is 
an overhead in the TCP/IP protocol etc. and ARP traffic etc (lots of it 
with MS), so 125M byte/s on 1G ethernet is impossible.

If you are running multiple applications using a single IDE disk for  
fileshares you will be lucky to use up even 10Mbit ethernet. 133MHz ATA 
or SATA hyped speed etc neglects the track to track seek time and 
rotational latency of a single drive, also the "real" transfer speed on 
the drive rather than the bus /cache RAM for sustained video transfer 
etc, is related to encoding density and rotation speed. Modern disks the 
sectors are a fiction and they pack more at the outer edge, thus about 2 
or 3 times faster than innermost track.

For real multitasking /multiuser any 4 drive or higher RAID 5 HW likely 
beats best IDE single drive and even SW RAID 5 may perform better.


-- 
Mike