Time to write routing tables

Fairchild, Steve Steve.Fairchild at hp.com
Thu Feb 27 08:35:44 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* "Fairchild, Steve" <Steve.Fairchild at hp.com>
*
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Hugh,
=20
I don't think there is a way to pick who does the configuration.  =
Mainly
because an initiator cannot find out who else is in the domain
(especially as large as you describe) without doing the configuration =
of
the tables first to be able to reach the other devices.  So it is
simpler to say that all initiators "shall" go through the exercise.  If
the first initiator to configure the expander marked the configuration
as complete, when would it do it?  How are CHANGEs managed?
=20
As to your question about how long to configure something with 1000 end
devices.  If you allow a very generous delay of 5ms per device then it
would be 5 seconds for a single initiator to configure the entire
topology.  Multiple initiators would be configuring the topology in
parallel, so the time should not be additive.
=20
For a more reasonable topology of around 128 end devices and a couple =
of
initiators it would be less than 1 second.
Current parallel SCSI designs allow 250 ms to timeout selections for
attached devices on a single bus of 16 devices which would mean an =
empty
bus takes at least 3.75 seconds to indicate no devices are attached.
=20
So I don't think the configuration by each initiator is an overwhelming
burden.
=20
Thanks,
=20
Steven Fairchild=20
Senior Member Technical Staff=20
Hewlett-Packard Corporation=20
MS150901=20
20555 SH 249=20
Houston, TX 77070=20
281 514 6448=20
steve.fairchild at hp.com=20


-----Original Message-----
From: Hugh Curley [mailto:hcurley at indra.com]
Sent: Thursday, February 27, 2003 4:46 AM
To: t10 at t10.org
Subject: Time to write routing tables



If I understand the protocol correctly, when the domain powers on (or
when one or more devices are added), all the initiators will discover
the entire topology by using Discovery one phy at a time.  All
initiators will then write the complete routing table for each expander
that has a configurable routing table. =20
=20
Changing the standard from "all initiators shall discover and write the
routing table" to "all initiators should discover and write the routing
table" simply means that in some configurations will have no initiators
that do this, while in other configurations all initiators will still =
do
it.  When I purchase the equipment for my new SAS domain, I will
probably by all the initiators from the same vendor.  If brand X writes
the routing table, then all my initiators will attempt to do so.  If
brand Y does not write the routing table, then none of my initiators
will attempt to do so.
=20
Let us imagine a domain that uses only 8% of the total possible
connections; consisting of 100 initiators and 900 targets.  How long
will it take to do discovery and update the routing tables.
=20
Would it not be quicker if a single initiator was selected to create =
the
tables?  It could be the one with the highest SAS address, lowest SAS
address, or the first one there marks the table unconfigurable, or
places a reserve (similar to the SCSI Reserve) on the SMP target.
=20
Am I on target?
=20
Thanks,
=20
Hugh Curley
hcurley at indra.com =20
=20


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 Hugh,
  
 I=20 don't think there is a way to pick who does the = configuration.  Mainly=20 because an initiator cannot find out who else is in the domain = (especially as=20 large as you describe) without doing the configuration of the tables = first to be=20 able to reach the other devices.  So it is simpler to say that all = initiators "shall" go through the exercise.  If the = first initiator to=20 configure the expander marked the configuration as complete, when would = it do=20 it?  How are CHANGEs managed?
  
 As to=20 your question about how long to configure something with 1000 end = devices. =20 If you allow a very generous delay of 5ms per device then it would be 5 = seconds=20 for a single initiator to configure the entire topology.  Multiple = initiators would be configuring the topology in parallel, so the time = should not=20 be additive.
  
 For a=20 more reasonable topology of around 128 end devices and a couple of = initiators it=20 would be less than 1 second.
 Current parallel SCSI designs allow 250 ms to timeout = selections for=20 attached devices on a single bus of 16 devices which would mean an = empty bus=20 takes at least 3.75 seconds to indicate no devices are=20 attached.
  
 So I=20 don't think the configuration by each initiator is an overwhelming=20 burden.
  
 Thanks,
  
 Steven=20 Fairchild 
Senior Member = Technical=20 Staff 
Hewlett-Packard=20 Corporation 
MS150901 
20555 SH 249 
Houston, TX 77070 
281 514=20 6448 
steve.fairchild at hp.com=20 

-----Original Message-----
From: Hugh Curley=20 [mailto:hcurley at indra.com]
Sent: Thursday, February 27, = 2003 4:46=20 AM
To: t10 at t10.org
Subject: Time to write routing = tables


 If I understand the protocol = correctly, when the=20 domain powers on (or when one or more devices are added), all the = initiators=20 will discover the entire topology by using Discovery one phy at a = time. =20 All initiators will then write the complete routing table for each = expander=20 that has a configurable routing table.  
 
 Changing the standard from "all initiators shall discover and = write=20 the routing table" to "all initiators should discover and write=20 the routing table" simply means that in some configurations will = have no=20 initiators that do this, while in other configurations all initiators = will=20 still do it.  When I purchase the equipment for my new SAS = domain, I will=20 probably by all the initiators from the same vendor.  If brand X = writes=20 the routing table, then all my initiators will attempt to do = so.  If=20 brand Y does not write the routing table, then none of my initiators = will=20 attempt to do so.
  
 Let us imagine a domain that uses = only 8% of the=20 total possible connections; consisting of 100 initiators and 900=20 targets.  How long will it take to do discovery and update the = routing=20 tables.
  
 Would it not be quicker if a single = initiator was=20 selected to create the tables?  It could be the one with the = highest SAS=20 address, lowest SAS address, or the first one there marks the table=20 unconfigurable, or places a reserve (similar to the SCSI Reserve) on = the SMP=20 target.
  
 Am I on target?
  
 Thanks,
  
 Hugh Curley
 hcurley at indra.com
  



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