I also use LTO7.
My disks are the most busy during a save.
Disk response increases 8x or more.
Your DASD subsystem also is a major factor.
On our old P7 R&D LPAR with 10k spinny disks, backing up to LTO7, the disks could not keep up with the LTO7 tape, disk response time now also included wait time.
We're now on P9, 100% SSD, both LPARS.
Disk response time is still 8x during a save.
A while back I tested Virtual tape.
As Rob stated, it was slower, the disks were super busy.
Paul
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxxxxxxxx] On Behalf Of Rob Berendt
Sent: Monday, March 04, 2019 2:02 PM
To: Midrange Systems Technical Discussion
Subject: RE: Full save to virtual tape?
Keep in mind:
1 - An LTO7 is a fairly decent tape drive. It's nothing like a 1/4" cartridge, 3570 and other slow stuff.
2 - Saves are streaming operations. They are not random I/O, which is where disk really shines.
3 - When you are using the same disks your arms now have to move between the read of the system on disk, to the write of the virtual tape on disk. This tends to have an adverse impact on streaming operations.
-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Justin Taylor
Sent: Monday, March 4, 2019 1:41 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: RE: Full save to virtual tape?
It'll be on a single partition 914 with external drives in a single ASP writing to an LTO7.
I wouldn't expect virtual tape to be slower. I assumed it would always be faster, just maybe not enough of a gain to be worth the trouble. Interesting...
-----Original Message-----
From: Rob Berendt [mailto:rob@xxxxxxxxx]
Sent: Monday, March 04, 2019 12:22 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: RE: Full save to virtual tape?
Actually if you have a decent tape drive, using virtual tape may SLOW down the save. Unless you have your image catalogs on different disk arms, etc.
Using a DD2500 VTL.
Full system save using BRMS.
SYSTEM1:
% of Size in
Description Disk 1,000,000 bytes
User libraries 78.35 5929624.98
User directories 1.45 109477.48
Folders and documents .00 .94
QSYS .07 5293.17
Other IBM libraries .75 56549.56
Licensed Internal Code .52 39087.72
Temporary space 3.75 283452.15
Unused space 14.87 1125228.38
System internal objects .28 20979.37
Objects not in a library .00 .00
TOTAL 100.04 7569693.75
Four hours 27 minutes
SYSTEM2:
% of Size in
Description Disk 1,000,000 bytes
User libraries 2.81 132094.79
User directories 79.64 3741403.98
Folders and documents .00 .11
QSYS .05 2480.81
Other IBM libraries .44 20723.65
Licensed Internal Code .18 8241.15
Temporary space .73 34170.61
Unused space 16.12 757352.04
System internal objects .02 780.66
Objects not in a library .00 .00
TOTAL 99.99 4697247.80
Three hours 17 minutes.
--
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