Subject: RE: iSCSI- Questions about implementation of Multiple connections

From: "Yao, Xuebin" <[email-masked]>
Date: Mon, 10 Dec 2001 17:19:11 -0800

Menqiu,

(1) Multiple connections are common. They will provide better performance
and availability. Multiple connection is more likely invisible to your
application 
since there is still single session for your application. A lot of storage
application need the high availability. For iSCSI aspect, your network link
could 
be a weakest link and have multiple connections could help to reduce the
risk of single-path failure. If you don't choose to implement multiple
connection, you may need to implement multiple HBA solution for
muti-pathing/failover which is more like traditional storag flavor mode and
still achieve redundancy. But in that case, your application (like LVM, file
system) may need to aware of the duplicate path.
    You could have your multiple connections in either active-passive mode
or load-balancing mode. However, I didn't why you don't want to implement
mutiple TCP connections in load-balance mode which doesn't sound any more
difficult than active-passive case (which you mentioned, exception case). 

(2) Your target side will not be only a single hard drive.  I didn't see why
you want to just attach a single hard drive to network ? Are you going to
try to implement iSCSI on the single Hard Drive? 
    Most time, your target side will be a storage subsystem with intelligent
controller. Your drive tray/JBOD or RAID system (in your word, the box)
should have the iSCSI target module or you can use a iSCSI to SCSI/FC router
to do that. 
    Even you don't have the scalibility to put multiple network portal on
your target side, you single network interface with even one IP can still
handle TCP multiple connections. Only drawback is, now the single point of
failure comes to your single network interface.

Xuebin Yao

>-----Original Message-----
>From: Mengqiu Wang [mailto:[email-masked]]
>Sent: Monday, December 10, 2001 12:29 AM
>To: [email-masked]
>Subject: Questions about implementation of Multiple connections

> I have several questions about multiple connections:

>(1) Are multiple connections between initiator and a
>target common? I mean, how many applications will
>require iSCSI implementation to be able to handle
>multiple connections within a session? Can anybody
>give me some overview idea about the application of
>multiple TCP connections, like: is it an exceptional
>case? or common case?

>(2) Consider a hard drive on the network. It only has
>one hardware port. If we want to develop a iSCSI box
>to handle all incoming iSCSI commands for it, is it
>necessary for the box to handle multiple TCP
>connections for this hard drive? How? Does the box
>need more than one IP addresses?

>Thanks,
>Meng

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