Hi

Interesting but have you made allowance for hardware compression?
Are you measuring the compressability rate of all those "zeroes"?
Where is the bottleneck - at  the tapehead or compression firmware?
Try the same exercise with data that has been already compressed.

Regards
Jim McDonald

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"Shafto, Eric" <Eric.Shafto AT drkw DOT com>@mailman.eng.auburn.edu on 
04/26/2003
12:42:50 AM

Sent by:    veritas-bu-admin AT mailman.eng.auburn DOT edu


To:    "'Paul Winkeler'" <pwinkeler AT pbnj-solutions DOT com>, "'Vijay Korde'"
       <vijay_korde AT hotmail DOT com>
cc:    veritas-bu AT mailman.eng.auburn DOT edu
Subject:    RE: [Veritas-bu] PCI bus and HBA throughput



It  would be interesting to see whether the situation improves noticeably
with  multiple HBAs. Does anyone have some data to share?
-----Original Message-----
From: Paul Winkeler  [mailto:pwinkeler AT pbnj-solutions DOT com]
Sent: Friday, April 25, 2003  8:57 AM
To: 'Vijay Korde'
Cc:  veritas-bu AT mailman.eng.auburn DOT edu
Subject: RE: [Veritas-bu] PCI bus  and HBA throughput


Hi  Vijay

Here  is what we found using two other brands of PCI Bus 2Gbit HBA's in
SunFire  880's going to T9904B's:
1)  To a single drive using 2Gbit HBA's, observed peak ~40MByte/sec,
regardless of  33 or 66Mhz bus
2)  Writing 3 streams to 3 drives across the same 2Gbit HBA, observed peak
~100MByte/sec regardless of 33 or 66Mhz bus
During all tests source data was fully cached in RAM  (machine had 8GByte)
and no other processes running (machine had 8  CPU's)

Wconcluded that the bottleneck was likely in the  handling of the SAN
protocols across the HBA.  Our basis for this  conclusion was this:
-  Writing zeroes (/dev/zero) to a single T9940B drive yielded a rate of
69MByte/sec which is basically the upper limit at which StorageTek claims
the  drive can take data in; so we know it can go that fast.
-  Pushing zeroes to 2 drives simultaneously can be done at an aggregate
rate of ~130MByte/sec on the 66MHz bus, closer to ~120MByte/sec on the
33Mhz  bus.
-  Going to 3 simultaneous drives with zeroes yields rates of ~138MByte/sec
and  129MByte/sec respectivel for the 66MHz and 33Mhz buses.
In  other words, the bus speed gave the 66Mhz bus a slight edge but hardly
worth  bothering.  It would be very interesting to see what the results
look  like when you use multiple HBA's simultaneously...

My  advice: don't hang more than 2 drives of a single HBA.

PaulW
www.pbnj-solutions.com IT Solutions  That Stick


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