In my experience a VTL can allow the Fibre line to saturate since it accepts
data (particularly those with SSD storage) at almost planer board speeds.
So yes, a properly sized VTL in your case could use the 16Gb particularly if
you are saving more than one partition at a time.

Yes it does depend a bit on the VTL vendor since all of them are engineered
a little differently.

--
Jim Oberholtzer
Agile Technology Architects

-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of
Steinmetz, Paul via MIDRANGE-L
Sent: Thursday, January 30, 2020 1:25 PM
To: 'Midrange Systems Technical Discussion' <midrange-l@xxxxxxxxxxxxxxxxxx>
Cc: Steinmetz, Paul <PSteinmetz@xxxxxxxxxx>
Subject: RE: VTL - Fiber vs SAS

Larry,

P9 9009-42A 100% SSD
Currently have an 3573 with 4 LTO7 HH FC drives connected from 2 LPARS via a
Cisco 9148 FC switch.
Each LPAR has a EN0A PCIe3 16Gb 2-port Fibre Channel Adapter.
We're using both ports from the ENOA.
Each port uses 2 drives.
Switch is zoned so that each LPAR can see all 4 drives.

The SSD are most busy during a save.
The SSD response time goes from .1 to .8 during a save.
This was much worse with old spinny disks, (tape was waiting on the disks)

Back when we had LTO5 and from an old PMR, An LTO5 drive will use 65% (per
IBM support) of the 8 gb bandwith (5.2 gb), leaving only 35% (2.8 gb) for
the 2nd drive.

It would be interesting to know how much bandwith a VTL would use and what
determines the bandwith with a VTL.
Will a VTL use the full 16 gb bandwith?
Or does this depend on the VTL vendor?

Paul

-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of
DrFranken
Sent: Thursday, January 30, 2020 8:44 AM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: VTL - Fiber vs SAS

You are correct that 4 LTO6 drives all in all out max compressed throughput
is roughly 13Gb per second. This is 2/3rs more than a single 8G port can
support.

However it would be quite rare for most IBM i customers to have a
sufficiently sized system to drive those drives to that level!!

That said, if you've invested in four drives you likely have a pretty big
system and should do your homework on port speed, and for that matter the
PCI-e Slot speed you're using!!

For THE VAST Majority of IBM i customers upgrading their tape drive beyond
LTO6 is likely to result in zero reduction in backup time. Most wouldn't
notice anything above LTO5. They just don't have the I/O infrastructure to
push it.

Only reason I bring this up is I hate to see customers investing in LTO7
drives (And $50+ Tapes) along with 16Gb Fiber ports when a SAS card with
LTO5 drive (And $20 tapes) will do the backup in the same time!

- Larry "DrFranken" Bolhuis

www.Frankeni.com
www.iDevCloud.com - Personal Development IBM i timeshare service.
www.iInTheCloud.com - Commercial IBM i Cloud Hosting.

On 1/30/2020 8:10 AM, Holger Scherer wrote:
right. Then also not to forget to have the IBM i host have multiple NPIV
capable ports to gain faster speed.
It's of not much use to have one 8GBit fiber port on the host and 4
fast LTO6 drives with one 8GBit (or faster) port for each drive. Been
there, done that ;-) -h

Am 30.01.2020 um 13:59 schrieb Rob Berendt <rob@xxxxxxxxx>:

One big difference between a VTL and one of those IBM 3xxx series
physical libraries with multiple drives is that the VTL uses a single port
on the NPIV capable switch even if it has multiple tape drives configured in
it. The physical library has you run a separate cable from each drive in
the library to the NPIV switch.


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