That is well summed up Vernon, the key concept being 2 LTO3
drives (and even 2 LTO2 drives) can "eat" a gigabit NIC all
on there own.

That said, I'd like to add that looking at PCI buses for the HBAs and/or 
NICs I'm always hard pressed to pick a particular SUN server up to the 
task.  Perhaps others can reccommend one?  The ideal server being one
where every card is connected to a seperate high speed PCI bus.

Also, it has been seen that Solaris 9 or Solaris 10 is needed to get 
the throughput out of mulitple NICS.

Robert Maiello
Pioneer Data Systems



On Tue, 14 Feb 2006 15:34:25 -0800, Vernon Harris <harriv00 AT YAHOO DOT COM> 
wrote:

>Ty,
>Rule of thumb for sizing a sun server to drive 4 x
>LTO3 drives would be as follows:
>
>   For each LTO-3 drive you would need a minimum of
>approximately 1.25GHZ of processing power.  That would
>include the processing power necessary to handle 1
>gigabit ethernet nic card.  But to adequately drive
>the 4 LTO-3 drives if you backup methodology is lan
>based backups, you should consider adding a second nic
>card and trunking the 2 nic cards together to create a
>fat network pipe.  Otherwise max throughput would be
>limited to approximately 80-90MB/sec, which is the
>practical thruput limit of gigabit ethernet. If you
>add a second nic, you will need 1.5GHZ of processor
>power per drive.
>
>Practically, most servers can never generate enough
>i/o to keep LTO-3 drives spooling without shoeshining
>the drives.  The installations that I've seen with
>LTO-3 drives configured attached to solaris servers
>have not expererienced performance issues on the
>servers.
>
>One important problem that I've seen repeatedly on Sun
>Servers attached to the fabric is with Sun Branded
>qlogic hba's using the leadville driver stack.  This
>is manifested with link offline errors in the
>/var/adm/messages file which causes the hba to go
>offline and the connected drives and libraries to
>disappear from the fabric.  This condition can only be
>resolved by rebooting the server.  Stick with native
>emulex or qlogic cards.  Otherwise you are asking for
>major problems.
>
>--- Ty Young <Phillip_Young AT I2 DOT COM> wrote:
>
>> All,
>>
>> I apologize in advance if this topic has been
>> covered.  I looked through
>> the archive using a variety of search terms without
>> successful results.
>>
>> We have determined that a 4 x LTO3 tape library will
>> work well in our
>> environment.    Our Sun SEs, however, claim that
>> attempting to drive such a
>> library with one host (i.e. where all four LTO3
>> drives are fiber-connected
>> through a switch into the server) is asking for
>> trouble and that we really
>> must consider driving it with two, in order to split
>> up the gigE network
>> bandwidth requirements as well as the FC HBA
>> bandwidth requirements.
>> Their argument seems to be based on the theoretical
>> maximum sustained I/O
>> that a Sun server backplane can handle, at 1.2
>> GB/sec.
>>
>> What I'm not understanding is how one calculates I/O
>> across a server.
>> Given that a server takes network traffic (input)
>> and routes it to the tape
>> drives (output), is it accurate to basically double
>> the aggregate
>> write-rate of a bunch of tape drives (read and
>> write) and then double that
>> number again to factor in performance with drive
>> compression ?
>>
>> My head is so full of numbers and stats at the
>> moment that I cannot think
>> straight and I need some help.   Thanks!
>>
>> -ty
>>
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