auto-rebuild RAID mirrors

Derek Atkins warlord at MIT.EDU
Mon Apr 30 11:02:03 EDT 2007


Mark Komarinski <mkomarinski at wayga.org> writes:

>> Wait, are you getting 20MB/s via NFS?  Or 20MB/s via Samba?
>> I'll note that 20MB/s is 160mbps, which is only about 23% of
>> the usable bandwidth of GigE.
>>   
> Just because the wire supports up to 1Gb, it doesn't mean that the whole
> stack of:
>
> disk
> memory
> CPU
> OS
> TCP/IP stack
> network drivers
> network card
> network switch
>
> will actually be able to push that much data.  My untuned testing on a
> 2.4 kernel a few years ago gave us about 300-500Mbps on a GigE system. 
> Tuning the kernel memory (and using 2.6?) can get you closer to 800Mbps,
> but that really relies on the amount of data you're sending.
>
> In case you're interested, using jumbo packets (9000MTU) doesn't
> necessarily improve network speed, but it does greatly reduce the CPU
> load on the sender and receiver.

I'll point out for the record that my 23% number above is:

   160/.23 == 695

I.e., I used a limit of 700mbps on a GigE.

> -Mark

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available


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