You make some good points.  Here are a few more things to consider.

Most vendors use .AWS format so there is compatibility at that level and that’s 
useful.  We have conversion utilities that allow us to replace another vendors 
VTL with the 5990.   As a wise person once said "indecision is the key to 
flexibility" which is why we also have the capability to limit volume size.  We 
actually have 1 customer that is running....it hurts to say it 3480 (which we 
also emulate) and we limit the volume size there for him. We find that most 
sites for whatever reason use 3490 with no max volume size even though we 
provide the capability to do other emulation and limit size.  Some sites do 
stack tapes and others put 1 dataset on a tape even though it’s a very small 
data set.  With VTL there is no wasted space so small datasets on a tape is not 
an issue.  
I believe that HSM will limit writing a tape to 97% (default value) of the 
specified tape type, so having unlimited volume size does not really affect 
anything.

Ken

Kenneth A. Bloom
CEO
Avenir Technologies Inc 
/d/b/a Visara International
203-984-2235
[email protected]
www.visara.com


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf 
Of R.S.
Sent: Wednesday, May 23, 2018 12:13 PM
To: [email protected]
Subject: Re: VTL as 3490 vs 3590

W dniu 2018-05-23 o 17:39, Mike Baldwin pisze:
[...]
 > Thanks for reading this far! Did I kill the thread?
No! Not at all.

 > A couple of the largest VTL vendors only support 3490
Well, can we enumerate the VTL vendors? IMHO all of them would be happy 
to see its name on the list, while it's still no advertisement.
Let me begin:
IBM TS7700 - does it support 3590 emulation? What volume sizes available?
VISARA Vi-5990 - according to Ken's informaton it does support 3590 
emulation, any volume size.
STK/Oracle VSM - only 3490?
EMC DLm - ???
what else?


Another thread:
Assuming maximum virtual volume size does NOT depend on emulation type 
(which is a case for VISARA) - what is an advantage of having 3590 over 
3490? And the opposite - what's wrong with 3590 emulation?

Compatibility: since both emulated 3490 and emulated 3590 are VIRTUAL 
and exist only inside VTL what problems could happen with "incompatible" 
drives? IMHO VISARA 150GB virtual volume is incompatible with Oracle VSM 
virtual volume despite of emulation type, however in any case it is 
perfectly possible to move data from one tape system to another. The 
largest (actual) volume size matter.


Optimal maximum volume size for HSM:
There are some limitations in HSM which do not allow to backup very 
large datasets because maximum number of tapes used for dump is limited 
to 254 (it was 40 in the past!). That clearly say the small volume size 
could pain.
What about upper values? Is it good or bad to have huge volumes? I'm 
using 4/12TB volumes (real TS1140) and see nothing wrong with it. Of 
course I cannot make the volume smaller4 times (yes, I know there are 
sport cartridges, but I have normal ones).
Getting back to VTLs - what would be wrong in using (potential) 12TB 
virtual volumes for HSM?
I do not insist on 12TB, but I'm trying to understand what the optimal 
value is and why.



Regards
-- 
Radoslaw Skorupka
Lodz, Poland




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