Andre,
At 02:32 PM 26/03/2003 -0800, Andre Hedrick wrote:
> > in reality, if you had multiple TCP streams, its more likely you're doing
> > it for high-availability reasons (i.e. multipathing).
> > if you're multipathing, the chances are you want to multipath down two
> > separate paths to two different iSCSI gateways. (assuming you're talking
> > to traditional SAN storage and you're gatewaying into Fibre Channel).
>
>Why a SAN gateway switch, they are all LAN limited.
?
hmm, where to start:
why a SAN gateway?
because (a) that's what is out there right now, (b) iSCSI is really the
enabler for people to connect to consolodated storage (that they already
have) at a cheaper price-point than FC.
LAN limited?
10GE is reality. so is etherchannel where you have 8xGE trunked
together. "LAN is limited" is a rather bold statement that doesn't support
the facts.
in reality, most applications do NOT want to push 100mbyte/sec of i/o -- or
even 20mbyte/sec.
sure -- benchmarking programs do -- and i could show you a single host
pushing 425mbyte/sec using 2 x 2gbit/s FC HBAs -- but in reality, thats way
overkill for most people.
i know that your company is working on native iSCSI storage arrays;
obviously its in your interests to talk about native iSCSI access to disks,
but right now, i'll talk about how people deploy TB of storage today. this
is most likely a different market segment to what you're working on (at
least i hope you think it is) - but a discussion on those merits are not
something that is useful in l-k.
> > handling multipathing in that manner is well beyond the scope of what an
> > iSCSI driver in the kernel should be doing.
> > determining the policy (read-preferred / write-preferred / round-robin /
> > ratio-of-i/o / sync-preferred+async-fallback / ...) on how those paths are
> > used is most definitely something that should NEVER be in the kernel.
>
>Only "NEVER" if you are depending on classic bloated SAN
>hardware/gateways. The very operations you are calling never, is done in
>the gateways which is nothing more or less than an embedded system on
>crack. So if this is an initiator which can manage sequencing streams, it
>is far superior than dealing with the SAN traps of today.
err, either you don't understand multipathing or i don't.
"multipathing" is end-to-end between an initiator and a target.
typically that initiator is a host and multipathing software is installed
on that host.
the target is typically a disk or disk-array. the disk array may have
multiple controllers and those show up as multiple targets.
the thing about multipathing is that it doesn't depend on any magic in "SAN
hardware/gateways" (sic) -- its simply a case of the host seeing the same
disk via two interfaces and choosing to use one/both of those interfaces to
talk to that disk.
[..]
>What do you have for real iSCSI and no FC junk not supporting
>interoperability?
?
no idea what you're talking about here.
>FC is dying and nobody who has wasted money on FC junk will be interested
>in iSCSI. They wasted piles of money and have to justify it.
lets just agree to disagree. i don't hold that view.
> > not bad for a single TCP stream and a software iSCSI stack. :-)
> > (kernel is 2.4.20)
>
>Nice numbers, now do it over WAN.
sustaining the throughput is simply a matter of:
- having a large enough TCP window
- ensuring all the TCP go-fast options are enabled
- ensuring you can have a sufficient number of IO operations outstanding
to allow SCSI to actually be able to fill the TCP window.
realistically, yes, this can sustain high throughput across a WAN. but
that WAN has to be built right in the first place.
i.e. if its moving other traffic, provide QoS to allow storage traffic to
have preference.
>Sweet kicker here, if you only allow the current rules of SAN to apply.
>This is what the big dogs want, and no new ideas allowed.
i definitely don't subscribe to your conspiracy theories here. sorry.
>PS poking back at you for fun and serious points.
yes - i figured. i'm happy to have a meaningful technical discussion, but
don't have the cycles to discuss the universe.
cheers,
lincoln.
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This archive was generated by hypermail 2b29 : Mon Mar 31 2003 - 22:00:26 EST