Networker

Re: [Networker] sizing a Sun server for a 4xLTO3 tape library

2006-02-14 18:37:58
Subject: Re: [Networker] sizing a Sun server for a 4xLTO3 tape library
From: Vernon Harris <harriv00 AT YAHOO DOT COM>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Tue, 14 Feb 2006 15:34:25 -0800
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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