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?


-----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 - Personal Development IBM i timeshare service. - 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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