RE: Full save to virtual tape?

I started using virtual tape on an 810 iSeries running v5r4. At the time, the performance difference was night-and-day. I've been a believer since. That initial experience is dated and could probably use with a good reassessment.

For daily backups, we take the system into a pseudo-restricted state and backup to virtual tape. Then we bring all the subsystems back online and dupe to 1 or 2 physical tapes.


I was hoping to shorten my periodic maintenance window on the new server with virtual tape. The consensus is that that's a pipe dream.


Thanks


-----Original Message-----
From: DrFranken [mailto:midrange@xxxxxxxxxxxx]
Sent: Monday, March 04, 2019 1:53 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: Full save to virtual tape?

I believe you can, but can you restore a full save from it? No. Thus you would then have to DUPTAP that to LTO or other external solution for it to have any real value.

It will consume a LOT of disk space, pretty much as much as you are using today. (GO figure!) You could do compression but that will be software compression meaning the system CPU is doing it thus slowing everything down.

As others have mentioned it will be competing with the backup for the same drives. So given almost no system with 1 core of IBM i can keep up with an LTO7 or even LTO6 drive because the disk subsystem is not robust enough. Now add the writing to the virtual tape on those drives and you might actually DOUBLE the time the backup takes.

Thus far I have yet to see virtual tape on IBM i beat the performance of a properly selected LTO device, not even close.

IBM says in their doco: "Your backups will be faster." But I was present when they announced this stuff. We asked "REALLY?" they said "Yes, equivalent to 2 or 3x!" We then asked: "Soooo how many DASD Units in your test?" IBM said: "Only about 300 (THREE HUNDRED) it's all we had available during the test." (face plant) Who has 300 disks in their system that are all only half full!?!

Now on the flipside there are still benefits. 1) You have this backup on disk. So if silly Sally in accounting smokes a table you can restore it el-quicko because the backup is sitting right there. No searching for tape from last night. 2) Once that DUPTAP is completed you can move it off-site straightaway and yet you still have an on-site copy there for your use.

So consider the pros and the cons for your shop.

- Larry "DrFranken" Bolhuis

www.Frankeni.com
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