Re: [PLUG] Disk Transfer Speeds

[PaulNM <plug@paulscrap.com>]

Brian Stempin wrote:
> Oh, one other thing:
> 
> Are you being careful between M*Bits* and M*Bytes*?  There's a pretty large
> difference.  A 100Mbit/sec connection = 12.5 MBytes/sec (remember:  there
> are 8 bits per byte).  Once you count in TCP/IP overhead (usually between
> 15% and 25%, depending on who you ask, jumbo frame settinsg, etc),
> 9MBytes/sec is a fair throughput.  I want to say that the fastest I've ever
> gotten on a 100Mbit connection was around 10.2MBytes/sec.
> 

Not to be pedantic, but it's actually 100Mbit/sec = 11.920929 
MBytes/sec. Bits are decimal while bytes are binary.

100Mbit = 100,000,000 bits (1^8)
100,000,000 / 8 = 12500000 bytes
12500000 / 1024 = 12207.031 KBytes
12207.031 / 1024 = 11.920929 MBytes

In this case it isn't much of a difference (592.9687 KBytes/sec), but 
once you get to Gbits and 10Gbits it is significant.

1 Gbit / 8 = .125 GBytes vs
(((1000000000/8)/1024)/1024)/1024 = 0.11641532 GBytes

Thats a roughly 8.79 MByte/sec difference.
10 Gbit (1.25 vs 1.164) has an 88.064 MBytes/sec difference.

Of course all these figures are pre-overhead calculations. :)


PaulNM

Who, last week, just went though bit/sec to theoretical Bytes/sec 
calculations for various connections 
(usb/1394/eth/bluetooth/(p/s)ata/802.11x/etc)

-- 

Snape kills Trinity with Rosebud when she tells Jar Jar she's his mother.
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